ginac/pseries.cpp

   1 /** @file pseries.cpp
   2  *
   3  *  Implementation of class for extended truncated power series and
   4  *  methods for series expansion. */
   5
   6 /*
   7  *  GiNaC Copyright (C) 1999-2002 Johannes Gutenberg University Mainz, Germany
   8  *
   9  *  This program is free software; you can redistribute it and/or modify
  10  *  it under the terms of the GNU General Public License as published by
  11  *  the Free Software Foundation; either version 2 of the License, or
  12  *  (at your option) any later version.
  13  *
  14  *  This program is distributed in the hope that it will be useful,
  15  *  but WITHOUT ANY WARRANTY; without even the implied warranty of
  16  *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  17  *  GNU General Public License for more details.
  18  *
  19  *  You should have received a copy of the GNU General Public License
  20  *  along with this program; if not, write to the Free Software
  21  *  Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
  22  */
  23
  24 #include <iostream>
  25 #include <stdexcept>
  26
  27 #include "pseries.h"
  28 #include "add.h"
  29 #include "inifcns.h" // for Order function
  30 #include "lst.h"
  31 #include "mul.h"
  32 #include "power.h"
  33 #include "relational.h"
  34 #include "operators.h"
  35 #include "symbol.h"
  36 #include "print.h"
  37 #include "archive.h"
  38 #include "utils.h"
  39
  40 namespace GiNaC {
  41
  42 GINAC_IMPLEMENT_REGISTERED_CLASS(pseries, basic)
  43
  44
  45 /*
  46  *  Default ctor, dtor, copy ctor, assignment operator and helpers
  47  */
  48
  49 pseries::pseries() : inherited(TINFO_pseries) { }
  50
  51 void pseries::copy(const pseries &other)
  52 {
  53         inherited::copy(other);
  54         seq = other.seq;
  55         var = other.var;
  56         point = other.point;
  57 }
  58
  59 DEFAULT_DESTROY(pseries)
  60
  61
  62 /*
  63  *  Other ctors
  64  */
  65
  66 /** Construct pseries from a vector of coefficients and powers.
  67  *  expair.rest holds the coefficient, expair.coeff holds the power.
  68  *  The powers must be integers (positive or negative) and in ascending order;
  69  *  the last coefficient can be Order(_ex1) to represent a truncated,
  70  *  non-terminating series.
  71  *
  72  *  @param rel_  expansion variable and point (must hold a relational)
  73  *  @param ops_  vector of {coefficient, power} pairs (coefficient must not be zero)
  74  *  @return newly constructed pseries */
  75 pseries::pseries(const ex &rel_, const epvector &ops_) : basic(TINFO_pseries), seq(ops_)
  76 {
  77         GINAC_ASSERT(is_exactly_a<relational>(rel_));
  78         GINAC_ASSERT(is_exactly_a<symbol>(rel_.lhs()));
  79         point = rel_.rhs();
  80         var = rel_.lhs();
  81 }
  82
  83
  84 /*
  85  *  Archiving
  86  */
  87
  88 pseries::pseries(const archive_node &n, const lst &sym_lst) : inherited(n, sym_lst)
  89 {
  90         for (unsigned int i=0; true; ++i) {
  91                 ex rest;
  92                 ex coeff;
  93                 if (n.find_ex("coeff", rest, sym_lst, i) && n.find_ex("power", coeff, sym_lst, i))
  94                         seq.push_back(expair(rest, coeff));
  95                 else
  96                         break;
  97         }
  98         n.find_ex("var", var, sym_lst);
  99         n.find_ex("point", point, sym_lst);
 100 }
 101
 102 void pseries::archive(archive_node &n) const
 103 {
 104         inherited::archive(n);
 105         epvector::const_iterator i = seq.begin(), iend = seq.end();
 106         while (i != iend) {
 107                 n.add_ex("coeff", i->rest);
 108                 n.add_ex("power", i->coeff);
 109                 ++i;
 110         }
 111         n.add_ex("var", var);
 112         n.add_ex("point", point);
 113 }
 114
 115 DEFAULT_UNARCHIVE(pseries)
 116
 117 //////////
 118 // functions overriding virtual functions from base classes
 119 //////////
 120
 121 void pseries::print(const print_context & c, unsigned level) const
 122 {
 123         if (is_a<print_tree>(c)) {
 124
 125                 c.s << std::string(level, ' ') << class_name()
 126                     << std::hex << ", hash=0x" << hashvalue << ", flags=0x" << flags << std::dec
 127                     << std::endl;
 128                 unsigned delta_indent = static_cast<const print_tree &>(c).delta_indent;
 129                 unsigned num = seq.size();
 130                 for (unsigned i=0; i<num; ++i) {
 131                         seq[i].rest.print(c, level + delta_indent);
 132                         seq[i].coeff.print(c, level + delta_indent);
 133                         c.s << std::string(level + delta_indent, ' ') << "-----" << std::endl;
 134                 }
 135                 var.print(c, level + delta_indent);
 136                 point.print(c, level + delta_indent);
 137
 138         } else if (is_a<print_python_repr>(c)) {
 139                 c.s << class_name() << "(relational(";
 140                 var.print(c);
 141                 c.s << ',';
 142                 point.print(c);
 143                 c.s << "),[";
 144                 unsigned num = seq.size();
 145                 for (unsigned i=0; i<num; ++i) {
 146                         if (i)
 147                                 c.s << ',';
 148                         c.s << '(';
 149                         seq[i].rest.print(c);
 150                         c.s << ',';
 151                         seq[i].coeff.print(c);
 152                         c.s << ')';
 153                 }
 154                 c.s << "])";
 155         } else {
 156
 157                 if (precedence() <= level)
 158                         c.s << "(";
 159
 160                 std::string par_open = is_a<print_latex>(c) ? "{(" : "(";
 161                 std::string par_close = is_a<print_latex>(c) ? ")}" : ")";
 162
 163                 // objects of type pseries must not have any zero entries, so the
 164                 // trivial (zero) pseries needs a special treatment here:
 165                 if (seq.empty())
 166                         c.s << '0';
 167                 epvector::const_iterator i = seq.begin(), end = seq.end();
 168                 while (i != end) {
 169                         // print a sign, if needed
 170                         if (i != seq.begin())
 171                                 c.s << '+';
 172                         if (!is_order_function(i->rest)) {
 173                                 // print 'rest', i.e. the expansion coefficient
 174                                 if (i->rest.info(info_flags::numeric) &&
 175                                         i->rest.info(info_flags::positive)) {
 176                                         i->rest.print(c);
 177                                 } else {
 178                                         c.s << par_open;
 179                                         i->rest.print(c);
 180                                         c.s << par_close;
 181                                 }
 182                                 // print 'coeff', something like (x-1)^42
 183                                 if (!i->coeff.is_zero()) {
 184                                         if (is_a<print_latex>(c))
 185                                                 c.s << ' ';
 186                                         else
 187                                                 c.s << '*';
 188                                         if (!point.is_zero()) {
 189                                                 c.s << par_open;
 190                                                 (var-point).print(c);
 191                                                 c.s << par_close;
 192                                         } else
 193                                                 var.print(c);
 194                                         if (i->coeff.compare(_ex1)) {
 195                                                 if (is_a<print_python>(c))
 196                                                         c.s << "**";
 197                                                 else
 198                                                         c.s << '^';
 199                                                 if (i->coeff.info(info_flags::negative)) {
 200                                                         c.s << par_open;
 201                                                         i->coeff.print(c);
 202                                                         c.s << par_close;
 203                                                 } else {
 204                                                         if (is_a<print_latex>(c)) {
 205                                                                 c.s << '{';
 206                                                                 i->coeff.print(c);
 207                                                                 c.s << '}';
 208                                                         } else
 209                                                                 i->coeff.print(c);
 210                                                 }
 211                                         }
 212                                 }
 213                         } else
 214                                 Order(power(var-point,i->coeff)).print(c);
 215                         ++i;
 216                 }
 217
 218                 if (precedence() <= level)
 219                         c.s << ")";
 220         }
 221 }
 222
 223 int pseries::compare_same_type(const basic & other) const
 224 {
 225         GINAC_ASSERT(is_a<pseries>(other));
 226         const pseries &o = static_cast<const pseries &>(other);
 227
 228         // first compare the lengths of the series...
 229         if (seq.size()>o.seq.size())
 230                 return 1;
 231         if (seq.size()<o.seq.size())
 232                 return -1;
 233
 234         // ...then the expansion point...
 235         int cmpval = var.compare(o.var);
 236         if (cmpval)
 237                 return cmpval;
 238         cmpval = point.compare(o.point);
 239         if (cmpval)
 240                 return cmpval;
 241
 242         // ...and if that failed the individual elements
 243         epvector::const_iterator it = seq.begin(), o_it = o.seq.begin();
 244         while (it!=seq.end() && o_it!=o.seq.end()) {
 245                 cmpval = it->compare(*o_it);
 246                 if (cmpval)
 247                         return cmpval;
 248                 ++it;
 249                 ++o_it;
 250         }
 251
 252         // so they are equal.
 253         return 0;
 254 }
 255
 256 /** Return the number of operands including a possible order term. */
 257 unsigned pseries::nops(void) const
 258 {
 259         return seq.size();
 260 }
 261
 262 /** Return the ith term in the series when represented as a sum. */
 263 ex pseries::op(int i) const
 264 {
 265         if (i < 0 || unsigned(i) >= seq.size())
 266                 throw (std::out_of_range("op() out of range"));
 267         return seq[i].rest * power(var - point, seq[i].coeff);
 268 }
 269
 270 ex &pseries::let_op(int i)
 271 {
 272         throw (std::logic_error("let_op not defined for pseries"));
 273 }
 274
 275 /** Return degree of highest power of the series.  This is usually the exponent
 276  *  of the Order term.  If s is not the expansion variable of the series, the
 277  *  series is examined termwise. */
 278 int pseries::degree(const ex &s) const
 279 {
 280         if (var.is_equal(s)) {
 281                 // Return last exponent
 282                 if (seq.size())
 283                         return ex_to<numeric>((seq.end()-1)->coeff).to_int();
 284                 else
 285                         return 0;
 286         } else {
 287                 epvector::const_iterator it = seq.begin(), itend = seq.end();
 288                 if (it == itend)
 289                         return 0;
 290                 int max_pow = INT_MIN;
 291                 while (it != itend) {
 292                         int pow = it->rest.degree(s);
 293                         if (pow > max_pow)
 294                                 max_pow = pow;
 295                         ++it;
 296                 }
 297                 return max_pow;
 298         }
 299 }
 300
 301 /** Return degree of lowest power of the series.  This is usually the exponent
 302  *  of the leading term.  If s is not the expansion variable of the series, the
 303  *  series is examined termwise.  If s is the expansion variable but the
 304  *  expansion point is not zero the series is not expanded to find the degree.
 305  *  I.e.: (1-x) + (1-x)^2 + Order((1-x)^3) has ldegree(x) 1, not 0. */
 306 int pseries::ldegree(const ex &s) const
 307 {
 308         if (var.is_equal(s)) {
 309                 // Return first exponent
 310                 if (seq.size())
 311                         return ex_to<numeric>((seq.begin())->coeff).to_int();
 312                 else
 313                         return 0;
 314         } else {
 315                 epvector::const_iterator it = seq.begin(), itend = seq.end();
 316                 if (it == itend)
 317                         return 0;
 318                 int min_pow = INT_MAX;
 319                 while (it != itend) {
 320                         int pow = it->rest.ldegree(s);
 321                         if (pow < min_pow)
 322                                 min_pow = pow;
 323                         ++it;
 324                 }
 325                 return min_pow;
 326         }
 327 }
 328
 329 /** Return coefficient of degree n in power series if s is the expansion
 330  *  variable.  If the expansion point is nonzero, by definition the n=1
 331  *  coefficient in s of a+b*(s-z)+c*(s-z)^2+Order((s-z)^3) is b (assuming
 332  *  the expansion took place in the s in the first place).
 333  *  If s is not the expansion variable, an attempt is made to convert the
 334  *  series to a polynomial and return the corresponding coefficient from
 335  *  there. */
 336 ex pseries::coeff(const ex &s, int n) const
 337 {
 338         if (var.is_equal(s)) {
 339                 if (seq.empty())
 340                         return _ex0;
 341
 342                 // Binary search in sequence for given power
 343                 numeric looking_for = numeric(n);
 344                 int lo = 0, hi = seq.size() - 1;
 345                 while (lo <= hi) {
 346                         int mid = (lo + hi) / 2;
 347                         GINAC_ASSERT(is_exactly_a<numeric>(seq[mid].coeff));
 348                         int cmp = ex_to<numeric>(seq[mid].coeff).compare(looking_for);
 349                         switch (cmp) {
 350                                 case -1:
 351                                         lo = mid + 1;
 352                                         break;
 353                                 case 0:
 354                                         return seq[mid].rest;
 355                                 case 1:
 356                                         hi = mid - 1;
 357                                         break;
 358                                 default:
 359                                         throw(std::logic_error("pseries::coeff: compare() didn't return -1, 0 or 1"));
 360                         }
 361                 }
 362                 return _ex0;
 363         } else
 364                 return convert_to_poly().coeff(s, n);
 365 }
 366
 367 /** Does nothing. */
 368 ex pseries::collect(const ex &s, bool distributed) const
 369 {
 370         return *this;
 371 }
 372
 373 /** Perform coefficient-wise automatic term rewriting rules in this class. */
 374 ex pseries::eval(int level) const
 375 {
 376         if (level == 1)
 377                 return this->hold();
 378
 379         if (level == -max_recursion_level)
 380                 throw (std::runtime_error("pseries::eval(): recursion limit exceeded"));
 381
 382         // Construct a new series with evaluated coefficients
 383         epvector new_seq;
 384         new_seq.reserve(seq.size());
 385         epvector::const_iterator it = seq.begin(), itend = seq.end();
 386         while (it != itend) {
 387                 new_seq.push_back(expair(it->rest.eval(level-1), it->coeff));
 388                 ++it;
 389         }
 390         return (new pseries(relational(var,point), new_seq))->setflag(status_flags::dynallocated | status_flags::evaluated);
 391 }
 392
 393 /** Evaluate coefficients numerically. */
 394 ex pseries::evalf(int level) const
 395 {
 396         if (level == 1)
 397                 return *this;
 398
 399         if (level == -max_recursion_level)
 400                 throw (std::runtime_error("pseries::evalf(): recursion limit exceeded"));
 401
 402         // Construct a new series with evaluated coefficients
 403         epvector new_seq;
 404         new_seq.reserve(seq.size());
 405         epvector::const_iterator it = seq.begin(), itend = seq.end();
 406         while (it != itend) {
 407                 new_seq.push_back(expair(it->rest.evalf(level-1), it->coeff));
 408                 ++it;
 409         }
 410         return (new pseries(relational(var,point), new_seq))->setflag(status_flags::dynallocated | status_flags::evaluated);
 411 }
 412
 413 ex pseries::subs(const lst & ls, const lst & lr, bool no_pattern) const
 414 {
 415         // If expansion variable is being substituted, convert the series to a
 416         // polynomial and do the substitution there because the result might
 417         // no longer be a power series
 418         if (ls.has(var))
 419                 return convert_to_poly(true).subs(ls, lr, no_pattern);
 420
 421         // Otherwise construct a new series with substituted coefficients and
 422         // expansion point
 423         epvector newseq;
 424         newseq.reserve(seq.size());
 425         epvector::const_iterator it = seq.begin(), itend = seq.end();
 426         while (it != itend) {
 427                 newseq.push_back(expair(it->rest.subs(ls, lr, no_pattern), it->coeff));
 428                 ++it;
 429         }
 430         return (new pseries(relational(var,point.subs(ls, lr, no_pattern)), newseq))->setflag(status_flags::dynallocated);
 431 }
 432
 433 /** Implementation of ex::expand() for a power series.  It expands all the
 434  *  terms individually and returns the resulting series as a new pseries. */
 435 ex pseries::expand(unsigned options) const
 436 {
 437         epvector newseq;
 438         epvector::const_iterator i = seq.begin(), end = seq.end();
 439         while (i != end) {
 440                 ex restexp = i->rest.expand();
 441                 if (!restexp.is_zero())
 442                         newseq.push_back(expair(restexp, i->coeff));
 443                 ++i;
 444         }
 445         return (new pseries(relational(var,point), newseq))
 446                 ->setflag(status_flags::dynallocated | (options == 0 ? status_flags::expanded : 0));
 447 }
 448
 449 /** Implementation of ex::diff() for a power series.
 450  *  @see ex::diff */
 451 ex pseries::derivative(const symbol & s) const
 452 {
 453         epvector new_seq;
 454         epvector::const_iterator it = seq.begin(), itend = seq.end();
 455
 456         if (s == var) {
 457
 458                 // FIXME: coeff might depend on var
 459                 while (it != itend) {
 460                         if (is_order_function(it->rest)) {
 461                                 new_seq.push_back(expair(it->rest, it->coeff - 1));
 462                         } else {
 463                                 ex c = it->rest * it->coeff;
 464                                 if (!c.is_zero())
 465                                         new_seq.push_back(expair(c, it->coeff - 1));
 466                         }
 467                         ++it;
 468                 }
 469
 470         } else {
 471
 472                 while (it != itend) {
 473                         if (is_order_function(it->rest)) {
 474                                 new_seq.push_back(*it);
 475                         } else {
 476                                 ex c = it->rest.diff(s);
 477                                 if (!c.is_zero())
 478                                         new_seq.push_back(expair(c, it->coeff));
 479                         }
 480                         ++it;
 481                 }
 482         }
 483
 484         return pseries(relational(var,point), new_seq);
 485 }
 486
 487 ex pseries::convert_to_poly(bool no_order) const
 488 {
 489         ex e;
 490         epvector::const_iterator it = seq.begin(), itend = seq.end();
 491
 492         while (it != itend) {
 493                 if (is_order_function(it->rest)) {
 494                         if (!no_order)
 495                                 e += Order(power(var - point, it->coeff));
 496                 } else
 497                         e += it->rest * power(var - point, it->coeff);
 498                 ++it;
 499         }
 500         return e;
 501 }
 502
 503 bool pseries::is_terminating(void) const
 504 {
 505         return seq.empty() || !is_order_function((seq.end()-1)->rest);
 506 }
 507
 508
 509 /*
 510  *  Implementations of series expansion
 511  */
 512
 513 /** Default implementation of ex::series(). This performs Taylor expansion.
 514  *  @see ex::series */
 515 ex basic::series(const relational & r, int order, unsigned options) const
 516 {
 517         epvector seq;
 518         numeric fac = 1;
 519         ex deriv = *this;
 520         ex coeff = deriv.subs(r);
 521         const symbol &s = ex_to<symbol>(r.lhs());
 522
 523         if (!coeff.is_zero())
 524                 seq.push_back(expair(coeff, _ex0));
 525
 526         int n;
 527         for (n=1; n<order; ++n) {
 528                 fac = fac.mul(n);
 529                 // We need to test for zero in order to see if the series terminates.
 530                 // The problem is that there is no such thing as a perfect test for
 531                 // zero.  Expanding the term occasionally helps a little...
 532                 deriv = deriv.diff(s).expand();
 533                 if (deriv.is_zero())  // Series terminates
 534                         return pseries(r, seq);
 535
 536                 coeff = deriv.subs(r);
 537                 if (!coeff.is_zero())
 538                         seq.push_back(expair(fac.inverse() * coeff, n));
 539         }
 540
 541         // Higher-order terms, if present
 542         deriv = deriv.diff(s);
 543         if (!deriv.expand().is_zero())
 544                 seq.push_back(expair(Order(_ex1), n));
 545         return pseries(r, seq);
 546 }
 547
 548
 549 /** Implementation of ex::series() for symbols.
 550  *  @see ex::series */
 551 ex symbol::series(const relational & r, int order, unsigned options) const
 552 {
 553         epvector seq;
 554         const ex point = r.rhs();
 555         GINAC_ASSERT(is_exactly_a<symbol>(r.lhs()));
 556
 557         if (this->is_equal_same_type(ex_to<symbol>(r.lhs()))) {
 558                 if (order > 0 && !point.is_zero())
 559                         seq.push_back(expair(point, _ex0));
 560                 if (order > 1)
 561                         seq.push_back(expair(_ex1, _ex1));
 562                 else
 563                         seq.push_back(expair(Order(_ex1), numeric(order)));
 564         } else
 565                 seq.push_back(expair(*this, _ex0));
 566         return pseries(r, seq);
 567 }
 568
 569
 570 /** Add one series object to another, producing a pseries object that
 571  *  represents the sum.
 572  *
 573  *  @param other  pseries object to add with
 574  *  @return the sum as a pseries */
 575 ex pseries::add_series(const pseries &other) const
 576 {
 577         // Adding two series with different variables or expansion points
 578         // results in an empty (constant) series
 579         if (!is_compatible_to(other)) {
 580                 epvector nul;
 581                 nul.push_back(expair(Order(_ex1), _ex0));
 582                 return pseries(relational(var,point), nul);
 583         }
 584
 585         // Series addition
 586         epvector new_seq;
 587         epvector::const_iterator a = seq.begin();
 588         epvector::const_iterator b = other.seq.begin();
 589         epvector::const_iterator a_end = seq.end();
 590         epvector::const_iterator b_end = other.seq.end();
 591         int pow_a = INT_MAX, pow_b = INT_MAX;
 592         for (;;) {
 593                 // If a is empty, fill up with elements from b and stop
 594                 if (a == a_end) {
 595                         while (b != b_end) {
 596                                 new_seq.push_back(*b);
 597                                 ++b;
 598                         }
 599                         break;
 600                 } else
 601                         pow_a = ex_to<numeric>((*a).coeff).to_int();
 602
 603                 // If b is empty, fill up with elements from a and stop
 604                 if (b == b_end) {
 605                         while (a != a_end) {
 606                                 new_seq.push_back(*a);
 607                                 ++a;
 608                         }
 609                         break;
 610                 } else
 611                         pow_b = ex_to<numeric>((*b).coeff).to_int();
 612
 613                 // a and b are non-empty, compare powers
 614                 if (pow_a < pow_b) {
 615                         // a has lesser power, get coefficient from a
 616                         new_seq.push_back(*a);
 617                         if (is_order_function((*a).rest))
 618                                 break;
 619                         ++a;
 620                 } else if (pow_b < pow_a) {
 621                         // b has lesser power, get coefficient from b
 622                         new_seq.push_back(*b);
 623                         if (is_order_function((*b).rest))
 624                                 break;
 625                         ++b;
 626                 } else {
 627                         // Add coefficient of a and b
 628                         if (is_order_function((*a).rest) || is_order_function((*b).rest)) {
 629                                 new_seq.push_back(expair(Order(_ex1), (*a).coeff));
 630                                 break;  // Order term ends the sequence
 631                         } else {
 632                                 ex sum = (*a).rest + (*b).rest;
 633                                 if (!(sum.is_zero()))
 634                                         new_seq.push_back(expair(sum, numeric(pow_a)));
 635                                 ++a;
 636                                 ++b;
 637                         }
 638                 }
 639         }
 640         return pseries(relational(var,point), new_seq);
 641 }
 642
 643
 644 /** Implementation of ex::series() for sums. This performs series addition when
 645  *  adding pseries objects.
 646  *  @see ex::series */
 647 ex add::series(const relational & r, int order, unsigned options) const
 648 {
 649         ex acc; // Series accumulator
 650
 651         // Get first term from overall_coeff
 652         acc = overall_coeff.series(r, order, options);
 653
 654         // Add remaining terms
 655         epvector::const_iterator it = seq.begin();
 656         epvector::const_iterator itend = seq.end();
 657         for (; it!=itend; ++it) {
 658                 ex op;
 659                 if (is_exactly_a<pseries>(it->rest))
 660                         op = it->rest;
 661                 else
 662                         op = it->rest.series(r, order, options);
 663                 if (!it->coeff.is_equal(_ex1))
 664                         op = ex_to<pseries>(op).mul_const(ex_to<numeric>(it->coeff));
 665
 666                 // Series addition
 667                 acc = ex_to<pseries>(acc).add_series(ex_to<pseries>(op));
 668         }
 669         return acc;
 670 }
 671
 672
 673 /** Multiply a pseries object with a numeric constant, producing a pseries
 674  *  object that represents the product.
 675  *
 676  *  @param other  constant to multiply with
 677  *  @return the product as a pseries */
 678 ex pseries::mul_const(const numeric &other) const
 679 {
 680         epvector new_seq;
 681         new_seq.reserve(seq.size());
 682
 683         epvector::const_iterator it = seq.begin(), itend = seq.end();
 684         while (it != itend) {
 685                 if (!is_order_function(it->rest))
 686                         new_seq.push_back(expair(it->rest * other, it->coeff));
 687                 else
 688                         new_seq.push_back(*it);
 689                 ++it;
 690         }
 691         return pseries(relational(var,point), new_seq);
 692 }
 693
 694
 695 /** Multiply one pseries object to another, producing a pseries object that
 696  *  represents the product.
 697  *
 698  *  @param other  pseries object to multiply with
 699  *  @return the product as a pseries */
 700 ex pseries::mul_series(const pseries &other) const
 701 {
 702         // Multiplying two series with different variables or expansion points
 703         // results in an empty (constant) series
 704         if (!is_compatible_to(other)) {
 705                 epvector nul;
 706                 nul.push_back(expair(Order(_ex1), _ex0));
 707                 return pseries(relational(var,point), nul);
 708         }
 709
 710         // Series multiplication
 711         epvector new_seq;
 712         int a_max = degree(var);
 713         int b_max = other.degree(var);
 714         int a_min = ldegree(var);
 715         int b_min = other.ldegree(var);
 716         int cdeg_min = a_min + b_min;
 717         int cdeg_max = a_max + b_max;
 718
 719         int higher_order_a = INT_MAX;
 720         int higher_order_b = INT_MAX;
 721         if (is_order_function(coeff(var, a_max)))
 722                 higher_order_a = a_max + b_min;
 723         if (is_order_function(other.coeff(var, b_max)))
 724                 higher_order_b = b_max + a_min;
 725         int higher_order_c = std::min(higher_order_a, higher_order_b);
 726         if (cdeg_max >= higher_order_c)
 727                 cdeg_max = higher_order_c - 1;
 728
 729         for (int cdeg=cdeg_min; cdeg<=cdeg_max; ++cdeg) {
 730                 ex co = _ex0;
 731                 // c(i)=a(0)b(i)+...+a(i)b(0)
 732                 for (int i=a_min; cdeg-i>=b_min; ++i) {
 733                         ex a_coeff = coeff(var, i);
 734                         ex b_coeff = other.coeff(var, cdeg-i);
 735                         if (!is_order_function(a_coeff) && !is_order_function(b_coeff))
 736                                 co += a_coeff * b_coeff;
 737                 }
 738                 if (!co.is_zero())
 739                         new_seq.push_back(expair(co, numeric(cdeg)));
 740         }
 741         if (higher_order_c < INT_MAX)
 742                 new_seq.push_back(expair(Order(_ex1), numeric(higher_order_c)));
 743         return pseries(relational(var, point), new_seq);
 744 }
 745
 746
 747 /** Implementation of ex::series() for product. This performs series
 748  *  multiplication when multiplying series.
 749  *  @see ex::series */
 750 ex mul::series(const relational & r, int order, unsigned options) const
 751 {
 752         pseries acc; // Series accumulator
 753
 754         // Multiply with remaining terms
 755         const epvector::const_iterator itbeg = seq.begin();
 756         const epvector::const_iterator itend = seq.end();
 757         for (epvector::const_iterator it=itbeg; it!=itend; ++it) {
 758                 ex op = recombine_pair_to_ex(*it).series(r, order, options);
 759
 760                 // Series multiplication
 761                 if (it==itbeg)
 762                         acc = ex_to<pseries>(op);
 763                 else
 764                         acc = ex_to<pseries>(acc.mul_series(ex_to<pseries>(op)));
 765         }
 766         return acc.mul_const(ex_to<numeric>(overall_coeff));
 767 }
 768
 769
 770 /** Compute the p-th power of a series.
 771  *
 772  *  @param p  power to compute
 773  *  @param deg  truncation order of series calculation */
 774 ex pseries::power_const(const numeric &p, int deg) const
 775 {
 776         // method:
 777         // (due to Leonhard Euler)
 778         // let A(x) be this series and for the time being let it start with a
 779         // constant (later we'll generalize):
 780         //     A(x) = a_0 + a_1*x + a_2*x^2 + ...
 781         // We want to compute
 782         //     C(x) = A(x)^p
 783         //     C(x) = c_0 + c_1*x + c_2*x^2 + ...
 784         // Taking the derivative on both sides and multiplying with A(x) one
 785         // immediately arrives at
 786         //     C'(x)*A(x) = p*C(x)*A'(x)
 787         // Multiplying this out and comparing coefficients we get the recurrence
 788         // formula
 789         //     c_i = (i*p*a_i*c_0 + ((i-1)*p-1)*a_{i-1}*c_1 + ...
 790         //                    ... + (p-(i-1))*a_1*c_{i-1})/(a_0*i)
 791         // which can easily be solved given the starting value c_0 = (a_0)^p.
 792         // For the more general case where the leading coefficient of A(x) is not
 793         // a constant, just consider A2(x) = A(x)*x^m, with some integer m and
 794         // repeat the above derivation.  The leading power of C2(x) = A2(x)^2 is
 795         // then of course x^(p*m) but the recurrence formula still holds.
 796
 797         if (seq.empty()) {
 798                 // as a special case, handle the empty (zero) series honoring the
 799                 // usual power laws such as implemented in power::eval()
 800                 if (p.real().is_zero())
 801                         throw std::domain_error("pseries::power_const(): pow(0,I) is undefined");
 802                 else if (p.real().is_negative())
 803                         throw pole_error("pseries::power_const(): division by zero",1);
 804                 else
 805                         return *this;
 806         }
 807
 808         const int ldeg = ldegree(var);
 809         if (!(p*ldeg).is_integer())
 810                 throw std::runtime_error("pseries::power_const(): trying to assemble a Puiseux series");
 811
 812         // O(x^n)^(-m) is undefined
 813         if (seq.size() == 1 && is_order_function(seq[0].rest) && p.real().is_negative())
 814                 throw pole_error("pseries::power_const(): division by zero",1);
 815
 816         // Compute coefficients of the powered series
 817         exvector co;
 818         co.reserve(deg);
 819         co.push_back(power(coeff(var, ldeg), p));
 820         bool all_sums_zero = true;
 821         for (int i=1; i<deg; ++i) {
 822                 ex sum = _ex0;
 823                 for (int j=1; j<=i; ++j) {
 824                         ex c = coeff(var, j + ldeg);
 825                         if (is_order_function(c)) {
 826                                 co.push_back(Order(_ex1));
 827                                 break;
 828                         } else
 829                                 sum += (p * j - (i - j)) * co[i - j] * c;
 830                 }
 831                 if (!sum.is_zero())
 832                         all_sums_zero = false;
 833                 co.push_back(sum / coeff(var, ldeg) / i);
 834         }
 835
 836         // Construct new series (of non-zero coefficients)
 837         epvector new_seq;
 838         bool higher_order = false;
 839         for (int i=0; i<deg; ++i) {
 840                 if (!co[i].is_zero())
 841                         new_seq.push_back(expair(co[i], p * ldeg + i));
 842                 if (is_order_function(co[i])) {
 843                         higher_order = true;
 844                         break;
 845                 }
 846         }
 847         if (!higher_order && !all_sums_zero)
 848                 new_seq.push_back(expair(Order(_ex1), p * ldeg + deg));
 849         return pseries(relational(var,point), new_seq);
 850 }
 851
 852
 853 /** Return a new pseries object with the powers shifted by deg. */
 854 pseries pseries::shift_exponents(int deg) const
 855 {
 856         epvector newseq = seq;
 857         epvector::iterator i = newseq.begin(), end  = newseq.end();
 858         while (i != end) {
 859                 i->coeff += deg;
 860                 ++i;
 861         }
 862         return pseries(relational(var, point), newseq);
 863 }
 864
 865
 866 /** Implementation of ex::series() for powers. This performs Laurent expansion
 867  *  of reciprocals of series at singularities.
 868  *  @see ex::series */
 869 ex power::series(const relational & r, int order, unsigned options) const
 870 {
 871         // If basis is already a series, just power it
 872         if (is_exactly_a<pseries>(basis))
 873                 return ex_to<pseries>(basis).power_const(ex_to<numeric>(exponent), order);
 874
 875         // Basis is not a series, may there be a singularity?
 876         bool must_expand_basis = false;
 877         try {
 878                 basis.subs(r);
 879         } catch (pole_error) {
 880                 must_expand_basis = true;
 881         }
 882
 883         // Is the expression of type something^(-int)?
 884         if (!must_expand_basis && !exponent.info(info_flags::negint))
 885                 return basic::series(r, order, options);
 886
 887         // Is the expression of type 0^something?
 888         if (!must_expand_basis && !basis.subs(r).is_zero())
 889                 return basic::series(r, order, options);
 890
 891         // Singularity encountered, is the basis equal to (var - point)?
 892         if (basis.is_equal(r.lhs() - r.rhs())) {
 893                 epvector new_seq;
 894                 if (ex_to<numeric>(exponent).to_int() < order)
 895                         new_seq.push_back(expair(_ex1, exponent));
 896                 else
 897                         new_seq.push_back(expair(Order(_ex1), exponent));
 898                 return pseries(r, new_seq);
 899         }
 900
 901         // No, expand basis into series
 902         ex e = basis.series(r, order, options);
 903         return ex_to<pseries>(e).power_const(ex_to<numeric>(exponent), order);
 904 }
 905
 906
 907 /** Re-expansion of a pseries object. */
 908 ex pseries::series(const relational & r, int order, unsigned options) const
 909 {
 910         const ex p = r.rhs();
 911         GINAC_ASSERT(is_exactly_a<symbol>(r.lhs()));
 912         const symbol &s = ex_to<symbol>(r.lhs());
 913
 914         if (var.is_equal(s) && point.is_equal(p)) {
 915                 if (order > degree(s))
 916                         return *this;
 917                 else {
 918                         epvector new_seq;
 919                         epvector::const_iterator it = seq.begin(), itend = seq.end();
 920                         while (it != itend) {
 921                                 int o = ex_to<numeric>(it->coeff).to_int();
 922                                 if (o >= order) {
 923                                         new_seq.push_back(expair(Order(_ex1), o));
 924                                         break;
 925                                 }
 926                                 new_seq.push_back(*it);
 927                                 ++it;
 928                         }
 929                         return pseries(r, new_seq);
 930                 }
 931         } else
 932                 return convert_to_poly().series(r, order, options);
 933 }
 934
 935
 936 /** Compute the truncated series expansion of an expression.
 937  *  This function returns an expression containing an object of class pseries
 938  *  to represent the series. If the series does not terminate within the given
 939  *  truncation order, the last term of the series will be an order term.
 940  *
 941  *  @param r  expansion relation, lhs holds variable and rhs holds point
 942  *  @param order  truncation order of series calculations
 943  *  @param options  of class series_options
 944  *  @return an expression holding a pseries object */
 945 ex ex::series(const ex & r, int order, unsigned options) const
 946 {
 947         GINAC_ASSERT(bp!=0);
 948         ex e;
 949         relational rel_;
 950
 951         if (is_exactly_a<relational>(r))
 952                 rel_ = ex_to<relational>(r);
 953         else if (is_exactly_a<symbol>(r))
 954                 rel_ = relational(r,_ex0);
 955         else
 956                 throw (std::logic_error("ex::series(): expansion point has unknown type"));
 957
 958         try {
 959                 e = bp->series(rel_, order, options);
 960         } catch (std::exception &x) {
 961                 throw (std::logic_error(std::string("unable to compute series (") + x.what() + ")"));
 962         }
 963         return e;
 964 }
 965
 966 } // namespace GiNaC