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) 1999-2003 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 "archive.h"
  37 #include "utils.h"
  38
  39 namespace GiNaC {
  40
  41 GINAC_IMPLEMENT_REGISTERED_CLASS_OPT(pseries, basic,
  42   print_func<print_context>(&pseries::do_print).
  43   print_func<print_latex>(&pseries::do_print_latex).
  44   print_func<print_tree>(&pseries::do_print_tree).
  45   print_func<print_python>(&pseries::do_print_python).
  46   print_func<print_python_repr>(&pseries::do_print_python_repr))
  47
  48
  49 /*
  50  *  Default constructor
  51  */
  52
  53 pseries::pseries() : inherited(TINFO_pseries) { }
  54
  55
  56 /*
  57  *  Other ctors
  58  */
  59
  60 /** Construct pseries from a vector of coefficients and powers.
  61  *  expair.rest holds the coefficient, expair.coeff holds the power.
  62  *  The powers must be integers (positive or negative) and in ascending order;
  63  *  the last coefficient can be Order(_ex1) to represent a truncated,
  64  *  non-terminating series.
  65  *
  66  *  @param rel_  expansion variable and point (must hold a relational)
  67  *  @param ops_  vector of {coefficient, power} pairs (coefficient must not be zero)
  68  *  @return newly constructed pseries */
  69 pseries::pseries(const ex &rel_, const epvector &ops_) : basic(TINFO_pseries), seq(ops_)
  70 {
  71         GINAC_ASSERT(is_a<relational>(rel_));
  72         GINAC_ASSERT(is_a<symbol>(rel_.lhs()));
  73         point = rel_.rhs();
  74         var = rel_.lhs();
  75 }
  76
  77
  78 /*
  79  *  Archiving
  80  */
  81
  82 pseries::pseries(const archive_node &n, lst &sym_lst) : inherited(n, sym_lst)
  83 {
  84         for (unsigned int i=0; true; ++i) {
  85                 ex rest;
  86                 ex coeff;
  87                 if (n.find_ex("coeff", rest, sym_lst, i) && n.find_ex("power", coeff, sym_lst, i))
  88                         seq.push_back(expair(rest, coeff));
  89                 else
  90                         break;
  91         }
  92         n.find_ex("var", var, sym_lst);
  93         n.find_ex("point", point, sym_lst);
  94 }
  95
  96 void pseries::archive(archive_node &n) const
  97 {
  98         inherited::archive(n);
  99         epvector::const_iterator i = seq.begin(), iend = seq.end();
 100         while (i != iend) {
 101                 n.add_ex("coeff", i->rest);
 102                 n.add_ex("power", i->coeff);
 103                 ++i;
 104         }
 105         n.add_ex("var", var);
 106         n.add_ex("point", point);
 107 }
 108
 109 DEFAULT_UNARCHIVE(pseries)
 110
 111 //////////
 112 // functions overriding virtual functions from base classes
 113 //////////
 114
 115 void pseries::print_series(const print_context & c, const char *openbrace, const char *closebrace, const char *mul_sym, const char *pow_sym, unsigned level) const
 116 {
 117         if (precedence() <= level)
 118                 c.s << '(';
 119
 120         // objects of type pseries must not have any zero entries, so the
 121         // trivial (zero) pseries needs a special treatment here:
 122         if (seq.empty())
 123                 c.s << '0';
 124
 125         epvector::const_iterator i = seq.begin(), end = seq.end();
 126         while (i != end) {
 127
 128                 // print a sign, if needed
 129                 if (i != seq.begin())
 130                         c.s << '+';
 131
 132                 if (!is_order_function(i->rest)) {
 133
 134                         // print 'rest', i.e. the expansion coefficient
 135                         if (i->rest.info(info_flags::numeric) &&
 136                                 i->rest.info(info_flags::positive)) {
 137                                 i->rest.print(c);
 138                         } else {
 139                                 c.s << openbrace << '(';
 140                                 i->rest.print(c);
 141                                 c.s << ')' << closebrace;
 142                         }
 143
 144                         // print 'coeff', something like (x-1)^42
 145                         if (!i->coeff.is_zero()) {
 146                                 c.s << mul_sym;
 147                                 if (!point.is_zero()) {
 148                                         c.s << openbrace << '(';
 149                                         (var-point).print(c);
 150                                         c.s << ')' << closebrace;
 151                                 } else
 152                                         var.print(c);
 153                                 if (i->coeff.compare(_ex1)) {
 154                                         c.s << pow_sym;
 155                                         c.s << openbrace;
 156                                         if (i->coeff.info(info_flags::negative)) {
 157                                                 c.s << '(';
 158                                                 i->coeff.print(c);
 159                                                 c.s << ')';
 160                                         } else
 161                                                 i->coeff.print(c);
 162                                         c.s << closebrace;
 163                                 }
 164                         }
 165                 } else
 166                         Order(power(var-point,i->coeff)).print(c);
 167                 ++i;
 168         }
 169
 170         if (precedence() <= level)
 171                 c.s << ')';
 172 }
 173
 174 void pseries::do_print(const print_context & c, unsigned level) const
 175 {
 176         print_series(c, "", "", "*", "^", level);
 177 }
 178
 179 void pseries::do_print_latex(const print_latex & c, unsigned level) const
 180 {
 181         print_series(c, "{", "}", " ", "^", level);
 182 }
 183
 184 void pseries::do_print_python(const print_python & c, unsigned level) const
 185 {
 186         print_series(c, "", "", "*", "**", level);
 187 }
 188
 189 void pseries::do_print_tree(const print_tree & c, unsigned level) const
 190 {
 191         c.s << std::string(level, ' ') << class_name()
 192             << std::hex << ", hash=0x" << hashvalue << ", flags=0x" << flags << std::dec
 193             << std::endl;
 194         size_t num = seq.size();
 195         for (size_t i=0; i<num; ++i) {
 196                 seq[i].rest.print(c, level + c.delta_indent);
 197                 seq[i].coeff.print(c, level + c.delta_indent);
 198                 c.s << std::string(level + c.delta_indent, ' ') << "-----" << std::endl;
 199         }
 200         var.print(c, level + c.delta_indent);
 201         point.print(c, level + c.delta_indent);
 202 }
 203
 204 void pseries::do_print_python_repr(const print_python_repr & c, unsigned level) const
 205 {
 206         c.s << class_name() << "(relational(";
 207         var.print(c);
 208         c.s << ',';
 209         point.print(c);
 210         c.s << "),[";
 211         size_t num = seq.size();
 212         for (size_t i=0; i<num; ++i) {
 213                 if (i)
 214                         c.s << ',';
 215                 c.s << '(';
 216                 seq[i].rest.print(c);
 217                 c.s << ',';
 218                 seq[i].coeff.print(c);
 219                 c.s << ')';
 220         }
 221         c.s << "])";
 222 }
 223
 224 int pseries::compare_same_type(const basic & other) const
 225 {
 226         GINAC_ASSERT(is_a<pseries>(other));
 227         const pseries &o = static_cast<const pseries &>(other);
 228
 229         // first compare the lengths of the series...
 230         if (seq.size()>o.seq.size())
 231                 return 1;
 232         if (seq.size()<o.seq.size())
 233                 return -1;
 234
 235         // ...then the expansion point...
 236         int cmpval = var.compare(o.var);
 237         if (cmpval)
 238                 return cmpval;
 239         cmpval = point.compare(o.point);
 240         if (cmpval)
 241                 return cmpval;
 242
 243         // ...and if that failed the individual elements
 244         epvector::const_iterator it = seq.begin(), o_it = o.seq.begin();
 245         while (it!=seq.end() && o_it!=o.seq.end()) {
 246                 cmpval = it->compare(*o_it);
 247                 if (cmpval)
 248                         return cmpval;
 249                 ++it;
 250                 ++o_it;
 251         }
 252
 253         // so they are equal.
 254         return 0;
 255 }
 256
 257 /** Return the number of operands including a possible order term. */
 258 size_t pseries::nops() const
 259 {
 260         return seq.size();
 261 }
 262
 263 /** Return the ith term in the series when represented as a sum. */
 264 ex pseries::op(size_t i) const
 265 {
 266         if (i >= seq.size())
 267                 throw (std::out_of_range("op() out of range"));
 268
 269         return seq[i].rest * power(var - point, seq[i].coeff);
 270 }
 271
 272 /** Return degree of highest power of the series.  This is usually the exponent
 273  *  of the Order term.  If s is not the expansion variable of the series, the
 274  *  series is examined termwise. */
 275 int pseries::degree(const ex &s) const
 276 {
 277         if (var.is_equal(s)) {
 278                 // Return last exponent
 279                 if (seq.size())
 280                         return ex_to<numeric>((seq.end()-1)->coeff).to_int();
 281                 else
 282                         return 0;
 283         } else {
 284                 epvector::const_iterator it = seq.begin(), itend = seq.end();
 285                 if (it == itend)
 286                         return 0;
 287                 int max_pow = INT_MIN;
 288                 while (it != itend) {
 289                         int pow = it->rest.degree(s);
 290                         if (pow > max_pow)
 291                                 max_pow = pow;
 292                         ++it;
 293                 }
 294                 return max_pow;
 295         }
 296 }
 297
 298 /** Return degree of lowest power of the series.  This is usually the exponent
 299  *  of the leading term.  If s is not the expansion variable of the series, the
 300  *  series is examined termwise.  If s is the expansion variable but the
 301  *  expansion point is not zero the series is not expanded to find the degree.
 302  *  I.e.: (1-x) + (1-x)^2 + Order((1-x)^3) has ldegree(x) 1, not 0. */
 303 int pseries::ldegree(const ex &s) const
 304 {
 305         if (var.is_equal(s)) {
 306                 // Return first exponent
 307                 if (seq.size())
 308                         return ex_to<numeric>((seq.begin())->coeff).to_int();
 309                 else
 310                         return 0;
 311         } else {
 312                 epvector::const_iterator it = seq.begin(), itend = seq.end();
 313                 if (it == itend)
 314                         return 0;
 315                 int min_pow = INT_MAX;
 316                 while (it != itend) {
 317                         int pow = it->rest.ldegree(s);
 318                         if (pow < min_pow)
 319                                 min_pow = pow;
 320                         ++it;
 321                 }
 322                 return min_pow;
 323         }
 324 }
 325
 326 /** Return coefficient of degree n in power series if s is the expansion
 327  *  variable.  If the expansion point is nonzero, by definition the n=1
 328  *  coefficient in s of a+b*(s-z)+c*(s-z)^2+Order((s-z)^3) is b (assuming
 329  *  the expansion took place in the s in the first place).
 330  *  If s is not the expansion variable, an attempt is made to convert the
 331  *  series to a polynomial and return the corresponding coefficient from
 332  *  there. */
 333 ex pseries::coeff(const ex &s, int n) const
 334 {
 335         if (var.is_equal(s)) {
 336                 if (seq.empty())
 337                         return _ex0;
 338
 339                 // Binary search in sequence for given power
 340                 numeric looking_for = numeric(n);
 341                 int lo = 0, hi = seq.size() - 1;
 342                 while (lo <= hi) {
 343                         int mid = (lo + hi) / 2;
 344                         GINAC_ASSERT(is_exactly_a<numeric>(seq[mid].coeff));
 345                         int cmp = ex_to<numeric>(seq[mid].coeff).compare(looking_for);
 346                         switch (cmp) {
 347                                 case -1:
 348                                         lo = mid + 1;
 349                                         break;
 350                                 case 0:
 351                                         return seq[mid].rest;
 352                                 case 1:
 353                                         hi = mid - 1;
 354                                         break;
 355                                 default:
 356                                         throw(std::logic_error("pseries::coeff: compare() didn't return -1, 0 or 1"));
 357                         }
 358                 }
 359                 return _ex0;
 360         } else
 361                 return convert_to_poly().coeff(s, n);
 362 }
 363
 364 /** Does nothing. */
 365 ex pseries::collect(const ex &s, bool distributed) const
 366 {
 367         return *this;
 368 }
 369
 370 /** Perform coefficient-wise automatic term rewriting rules in this class. */
 371 ex pseries::eval(int level) const
 372 {
 373         if (level == 1)
 374                 return this->hold();
 375
 376         if (level == -max_recursion_level)
 377                 throw (std::runtime_error("pseries::eval(): recursion limit exceeded"));
 378
 379         // Construct a new series with evaluated coefficients
 380         epvector new_seq;
 381         new_seq.reserve(seq.size());
 382         epvector::const_iterator it = seq.begin(), itend = seq.end();
 383         while (it != itend) {
 384                 new_seq.push_back(expair(it->rest.eval(level-1), it->coeff));
 385                 ++it;
 386         }
 387         return (new pseries(relational(var,point), new_seq))->setflag(status_flags::dynallocated | status_flags::evaluated);
 388 }
 389
 390 /** Evaluate coefficients numerically. */
 391 ex pseries::evalf(int level) const
 392 {
 393         if (level == 1)
 394                 return *this;
 395
 396         if (level == -max_recursion_level)
 397                 throw (std::runtime_error("pseries::evalf(): recursion limit exceeded"));
 398
 399         // Construct a new series with evaluated coefficients
 400         epvector new_seq;
 401         new_seq.reserve(seq.size());
 402         epvector::const_iterator it = seq.begin(), itend = seq.end();
 403         while (it != itend) {
 404                 new_seq.push_back(expair(it->rest.evalf(level-1), it->coeff));
 405                 ++it;
 406         }
 407         return (new pseries(relational(var,point), new_seq))->setflag(status_flags::dynallocated | status_flags::evaluated);
 408 }
 409
 410 ex pseries::subs(const exmap & m, unsigned options) const
 411 {
 412         // If expansion variable is being substituted, convert the series to a
 413         // polynomial and do the substitution there because the result might
 414         // no longer be a power series
 415         if (m.find(var) != m.end())
 416                 return convert_to_poly(true).subs(m, options);
 417
 418         // Otherwise construct a new series with substituted coefficients and
 419         // expansion point
 420         epvector newseq;
 421         newseq.reserve(seq.size());
 422         epvector::const_iterator it = seq.begin(), itend = seq.end();
 423         while (it != itend) {
 424                 newseq.push_back(expair(it->rest.subs(m, options), it->coeff));
 425                 ++it;
 426         }
 427         return (new pseries(relational(var,point.subs(m, options)), newseq))->setflag(status_flags::dynallocated);
 428 }
 429
 430 /** Implementation of ex::expand() for a power series.  It expands all the
 431  *  terms individually and returns the resulting series as a new pseries. */
 432 ex pseries::expand(unsigned options) const
 433 {
 434         epvector newseq;
 435         epvector::const_iterator i = seq.begin(), end = seq.end();
 436         while (i != end) {
 437                 ex restexp = i->rest.expand();
 438                 if (!restexp.is_zero())
 439                         newseq.push_back(expair(restexp, i->coeff));
 440                 ++i;
 441         }
 442         return (new pseries(relational(var,point), newseq))
 443                 ->setflag(status_flags::dynallocated | (options == 0 ? status_flags::expanded : 0));
 444 }
 445
 446 /** Implementation of ex::diff() for a power series.
 447  *  @see ex::diff */
 448 ex pseries::derivative(const symbol & s) const
 449 {
 450         epvector new_seq;
 451         epvector::const_iterator it = seq.begin(), itend = seq.end();
 452
 453         if (s == var) {
 454
 455                 // FIXME: coeff might depend on var
 456                 while (it != itend) {
 457                         if (is_order_function(it->rest)) {
 458                                 new_seq.push_back(expair(it->rest, it->coeff - 1));
 459                         } else {
 460                                 ex c = it->rest * it->coeff;
 461                                 if (!c.is_zero())
 462                                         new_seq.push_back(expair(c, it->coeff - 1));
 463                         }
 464                         ++it;
 465                 }
 466
 467         } else {
 468
 469                 while (it != itend) {
 470                         if (is_order_function(it->rest)) {
 471                                 new_seq.push_back(*it);
 472                         } else {
 473                                 ex c = it->rest.diff(s);
 474                                 if (!c.is_zero())
 475                                         new_seq.push_back(expair(c, it->coeff));
 476                         }
 477                         ++it;
 478                 }
 479         }
 480
 481         return pseries(relational(var,point), new_seq);
 482 }
 483
 484 ex pseries::convert_to_poly(bool no_order) const
 485 {
 486         ex e;
 487         epvector::const_iterator it = seq.begin(), itend = seq.end();
 488
 489         while (it != itend) {
 490                 if (is_order_function(it->rest)) {
 491                         if (!no_order)
 492                                 e += Order(power(var - point, it->coeff));
 493                 } else
 494                         e += it->rest * power(var - point, it->coeff);
 495                 ++it;
 496         }
 497         return e;
 498 }
 499
 500 bool pseries::is_terminating() const
 501 {
 502         return seq.empty() || !is_order_function((seq.end()-1)->rest);
 503 }
 504
 505
 506 /*
 507  *  Implementations of series expansion
 508  */
 509
 510 /** Default implementation of ex::series(). This performs Taylor expansion.
 511  *  @see ex::series */
 512 ex basic::series(const relational & r, int order, unsigned options) const
 513 {
 514         epvector seq;
 515         numeric fac = 1;
 516         ex deriv = *this;
 517         ex coeff = deriv.subs(r, subs_options::no_pattern);
 518         const symbol &s = ex_to<symbol>(r.lhs());
 519
 520         if (!coeff.is_zero())
 521                 seq.push_back(expair(coeff, _ex0));
 522
 523         int n;
 524         for (n=1; n<order; ++n) {
 525                 fac = fac.mul(n);
 526                 // We need to test for zero in order to see if the series terminates.
 527                 // The problem is that there is no such thing as a perfect test for
 528                 // zero.  Expanding the term occasionally helps a little...
 529                 deriv = deriv.diff(s).expand();
 530                 if (deriv.is_zero())  // Series terminates
 531                         return pseries(r, seq);
 532
 533                 coeff = deriv.subs(r, subs_options::no_pattern);
 534                 if (!coeff.is_zero())
 535                         seq.push_back(expair(fac.inverse() * coeff, n));
 536         }
 537
 538         // Higher-order terms, if present
 539         deriv = deriv.diff(s);
 540         if (!deriv.expand().is_zero())
 541                 seq.push_back(expair(Order(_ex1), n));
 542         return pseries(r, seq);
 543 }
 544
 545
 546 /** Implementation of ex::series() for symbols.
 547  *  @see ex::series */
 548 ex symbol::series(const relational & r, int order, unsigned options) const
 549 {
 550         epvector seq;
 551         const ex point = r.rhs();
 552         GINAC_ASSERT(is_a<symbol>(r.lhs()));
 553
 554         if (this->is_equal_same_type(ex_to<symbol>(r.lhs()))) {
 555                 if (order > 0 && !point.is_zero())
 556                         seq.push_back(expair(point, _ex0));
 557                 if (order > 1)
 558                         seq.push_back(expair(_ex1, _ex1));
 559                 else
 560                         seq.push_back(expair(Order(_ex1), numeric(order)));
 561         } else
 562                 seq.push_back(expair(*this, _ex0));
 563         return pseries(r, seq);
 564 }
 565
 566
 567 /** Add one series object to another, producing a pseries object that
 568  *  represents the sum.
 569  *
 570  *  @param other  pseries object to add with
 571  *  @return the sum as a pseries */
 572 ex pseries::add_series(const pseries &other) const
 573 {
 574         // Adding two series with different variables or expansion points
 575         // results in an empty (constant) series
 576         if (!is_compatible_to(other)) {
 577                 epvector nul;
 578                 nul.push_back(expair(Order(_ex1), _ex0));
 579                 return pseries(relational(var,point), nul);
 580         }
 581
 582         // Series addition
 583         epvector new_seq;
 584         epvector::const_iterator a = seq.begin();
 585         epvector::const_iterator b = other.seq.begin();
 586         epvector::const_iterator a_end = seq.end();
 587         epvector::const_iterator b_end = other.seq.end();
 588         int pow_a = INT_MAX, pow_b = INT_MAX;
 589         for (;;) {
 590                 // If a is empty, fill up with elements from b and stop
 591                 if (a == a_end) {
 592                         while (b != b_end) {
 593                                 new_seq.push_back(*b);
 594                                 ++b;
 595                         }
 596                         break;
 597                 } else
 598                         pow_a = ex_to<numeric>((*a).coeff).to_int();
 599
 600                 // If b is empty, fill up with elements from a and stop
 601                 if (b == b_end) {
 602                         while (a != a_end) {
 603                                 new_seq.push_back(*a);
 604                                 ++a;
 605                         }
 606                         break;
 607                 } else
 608                         pow_b = ex_to<numeric>((*b).coeff).to_int();
 609
 610                 // a and b are non-empty, compare powers
 611                 if (pow_a < pow_b) {
 612                         // a has lesser power, get coefficient from a
 613                         new_seq.push_back(*a);
 614                         if (is_order_function((*a).rest))
 615                                 break;
 616                         ++a;
 617                 } else if (pow_b < pow_a) {
 618                         // b has lesser power, get coefficient from b
 619                         new_seq.push_back(*b);
 620                         if (is_order_function((*b).rest))
 621                                 break;
 622                         ++b;
 623                 } else {
 624                         // Add coefficient of a and b
 625                         if (is_order_function((*a).rest) || is_order_function((*b).rest)) {
 626                                 new_seq.push_back(expair(Order(_ex1), (*a).coeff));
 627                                 break;  // Order term ends the sequence
 628                         } else {
 629                                 ex sum = (*a).rest + (*b).rest;
 630                                 if (!(sum.is_zero()))
 631                                         new_seq.push_back(expair(sum, numeric(pow_a)));
 632                                 ++a;
 633                                 ++b;
 634                         }
 635                 }
 636         }
 637         return pseries(relational(var,point), new_seq);
 638 }
 639
 640
 641 /** Implementation of ex::series() for sums. This performs series addition when
 642  *  adding pseries objects.
 643  *  @see ex::series */
 644 ex add::series(const relational & r, int order, unsigned options) const
 645 {
 646         ex acc; // Series accumulator
 647
 648         // Get first term from overall_coeff
 649         acc = overall_coeff.series(r, order, options);
 650
 651         // Add remaining terms
 652         epvector::const_iterator it = seq.begin();
 653         epvector::const_iterator itend = seq.end();
 654         for (; it!=itend; ++it) {
 655                 ex op;
 656                 if (is_exactly_a<pseries>(it->rest))
 657                         op = it->rest;
 658                 else
 659                         op = it->rest.series(r, order, options);
 660                 if (!it->coeff.is_equal(_ex1))
 661                         op = ex_to<pseries>(op).mul_const(ex_to<numeric>(it->coeff));
 662
 663                 // Series addition
 664                 acc = ex_to<pseries>(acc).add_series(ex_to<pseries>(op));
 665         }
 666         return acc;
 667 }
 668
 669
 670 /** Multiply a pseries object with a numeric constant, producing a pseries
 671  *  object that represents the product.
 672  *
 673  *  @param other  constant to multiply with
 674  *  @return the product as a pseries */
 675 ex pseries::mul_const(const numeric &other) const
 676 {
 677         epvector new_seq;
 678         new_seq.reserve(seq.size());
 679
 680         epvector::const_iterator it = seq.begin(), itend = seq.end();
 681         while (it != itend) {
 682                 if (!is_order_function(it->rest))
 683                         new_seq.push_back(expair(it->rest * other, it->coeff));
 684                 else
 685                         new_seq.push_back(*it);
 686                 ++it;
 687         }
 688         return pseries(relational(var,point), new_seq);
 689 }
 690
 691
 692 /** Multiply one pseries object to another, producing a pseries object that
 693  *  represents the product.
 694  *
 695  *  @param other  pseries object to multiply with
 696  *  @return the product as a pseries */
 697 ex pseries::mul_series(const pseries &other) const
 698 {
 699         // Multiplying two series with different variables or expansion points
 700         // results in an empty (constant) series
 701         if (!is_compatible_to(other)) {
 702                 epvector nul;
 703                 nul.push_back(expair(Order(_ex1), _ex0));
 704                 return pseries(relational(var,point), nul);
 705         }
 706
 707         // Series multiplication
 708         epvector new_seq;
 709         int a_max = degree(var);
 710         int b_max = other.degree(var);
 711         int a_min = ldegree(var);
 712         int b_min = other.ldegree(var);
 713         int cdeg_min = a_min + b_min;
 714         int cdeg_max = a_max + b_max;
 715
 716         int higher_order_a = INT_MAX;
 717         int higher_order_b = INT_MAX;
 718         if (is_order_function(coeff(var, a_max)))
 719                 higher_order_a = a_max + b_min;
 720         if (is_order_function(other.coeff(var, b_max)))
 721                 higher_order_b = b_max + a_min;
 722         int higher_order_c = std::min(higher_order_a, higher_order_b);
 723         if (cdeg_max >= higher_order_c)
 724                 cdeg_max = higher_order_c - 1;
 725
 726         for (int cdeg=cdeg_min; cdeg<=cdeg_max; ++cdeg) {
 727                 ex co = _ex0;
 728                 // c(i)=a(0)b(i)+...+a(i)b(0)
 729                 for (int i=a_min; cdeg-i>=b_min; ++i) {
 730                         ex a_coeff = coeff(var, i);
 731                         ex b_coeff = other.coeff(var, cdeg-i);
 732                         if (!is_order_function(a_coeff) && !is_order_function(b_coeff))
 733                                 co += a_coeff * b_coeff;
 734                 }
 735                 if (!co.is_zero())
 736                         new_seq.push_back(expair(co, numeric(cdeg)));
 737         }
 738         if (higher_order_c < INT_MAX)
 739                 new_seq.push_back(expair(Order(_ex1), numeric(higher_order_c)));
 740         return pseries(relational(var, point), new_seq);
 741 }
 742
 743
 744 /** Implementation of ex::series() for product. This performs series
 745  *  multiplication when multiplying series.
 746  *  @see ex::series */
 747 ex mul::series(const relational & r, int order, unsigned options) const
 748 {
 749         pseries acc; // Series accumulator
 750
 751         // Multiply with remaining terms
 752         const epvector::const_iterator itbeg = seq.begin();
 753         const epvector::const_iterator itend = seq.end();
 754         for (epvector::const_iterator it=itbeg; it!=itend; ++it) {
 755                 ex op = recombine_pair_to_ex(*it).series(r, order, options);
 756
 757                 // Series multiplication
 758                 if (it==itbeg)
 759                         acc = ex_to<pseries>(op);
 760                 else
 761                         acc = ex_to<pseries>(acc.mul_series(ex_to<pseries>(op)));
 762         }
 763         return acc.mul_const(ex_to<numeric>(overall_coeff));
 764 }
 765
 766
 767 /** Compute the p-th power of a series.
 768  *
 769  *  @param p  power to compute
 770  *  @param deg  truncation order of series calculation */
 771 ex pseries::power_const(const numeric &p, int deg) const
 772 {
 773         // method:
 774         // (due to Leonhard Euler)
 775         // let A(x) be this series and for the time being let it start with a
 776         // constant (later we'll generalize):
 777         //     A(x) = a_0 + a_1*x + a_2*x^2 + ...
 778         // We want to compute
 779         //     C(x) = A(x)^p
 780         //     C(x) = c_0 + c_1*x + c_2*x^2 + ...
 781         // Taking the derivative on both sides and multiplying with A(x) one
 782         // immediately arrives at
 783         //     C'(x)*A(x) = p*C(x)*A'(x)
 784         // Multiplying this out and comparing coefficients we get the recurrence
 785         // formula
 786         //     c_i = (i*p*a_i*c_0 + ((i-1)*p-1)*a_{i-1}*c_1 + ...
 787         //                    ... + (p-(i-1))*a_1*c_{i-1})/(a_0*i)
 788         // which can easily be solved given the starting value c_0 = (a_0)^p.
 789         // For the more general case where the leading coefficient of A(x) is not
 790         // a constant, just consider A2(x) = A(x)*x^m, with some integer m and
 791         // repeat the above derivation.  The leading power of C2(x) = A2(x)^2 is
 792         // then of course x^(p*m) but the recurrence formula still holds.
 793
 794         if (seq.empty()) {
 795                 // as a special case, handle the empty (zero) series honoring the
 796                 // usual power laws such as implemented in power::eval()
 797                 if (p.real().is_zero())
 798                         throw std::domain_error("pseries::power_const(): pow(0,I) is undefined");
 799                 else if (p.real().is_negative())
 800                         throw pole_error("pseries::power_const(): division by zero",1);
 801                 else
 802                         return *this;
 803         }
 804
 805         const int ldeg = ldegree(var);
 806         if (!(p*ldeg).is_integer())
 807                 throw std::runtime_error("pseries::power_const(): trying to assemble a Puiseux series");
 808
 809         // O(x^n)^(-m) is undefined
 810         if (seq.size() == 1 && is_order_function(seq[0].rest) && p.real().is_negative())
 811                 throw pole_error("pseries::power_const(): division by zero",1);
 812
 813         // Compute coefficients of the powered series
 814         exvector co;
 815         co.reserve(deg);
 816         co.push_back(power(coeff(var, ldeg), p));
 817         bool all_sums_zero = true;
 818         for (int i=1; i<deg; ++i) {
 819                 ex sum = _ex0;
 820                 for (int j=1; j<=i; ++j) {
 821                         ex c = coeff(var, j + ldeg);
 822                         if (is_order_function(c)) {
 823                                 co.push_back(Order(_ex1));
 824                                 break;
 825                         } else
 826                                 sum += (p * j - (i - j)) * co[i - j] * c;
 827                 }
 828                 if (!sum.is_zero())
 829                         all_sums_zero = false;
 830                 co.push_back(sum / coeff(var, ldeg) / i);
 831         }
 832
 833         // Construct new series (of non-zero coefficients)
 834         epvector new_seq;
 835         bool higher_order = false;
 836         for (int i=0; i<deg; ++i) {
 837                 if (!co[i].is_zero())
 838                         new_seq.push_back(expair(co[i], p * ldeg + i));
 839                 if (is_order_function(co[i])) {
 840                         higher_order = true;
 841                         break;
 842                 }
 843         }
 844         if (!higher_order && !all_sums_zero)
 845                 new_seq.push_back(expair(Order(_ex1), p * ldeg + deg));
 846         return pseries(relational(var,point), new_seq);
 847 }
 848
 849
 850 /** Return a new pseries object with the powers shifted by deg. */
 851 pseries pseries::shift_exponents(int deg) const
 852 {
 853         epvector newseq = seq;
 854         epvector::iterator i = newseq.begin(), end  = newseq.end();
 855         while (i != end) {
 856                 i->coeff += deg;
 857                 ++i;
 858         }
 859         return pseries(relational(var, point), newseq);
 860 }
 861
 862
 863 /** Implementation of ex::series() for powers. This performs Laurent expansion
 864  *  of reciprocals of series at singularities.
 865  *  @see ex::series */
 866 ex power::series(const relational & r, int order, unsigned options) const
 867 {
 868         // If basis is already a series, just power it
 869         if (is_exactly_a<pseries>(basis))
 870                 return ex_to<pseries>(basis).power_const(ex_to<numeric>(exponent), order);
 871
 872         // Basis is not a series, may there be a singularity?
 873         bool must_expand_basis = false;
 874         try {
 875                 basis.subs(r, subs_options::no_pattern);
 876         } catch (pole_error) {
 877                 must_expand_basis = true;
 878         }
 879
 880         // Is the expression of type something^(-int)?
 881         if (!must_expand_basis && !exponent.info(info_flags::negint))
 882                 return basic::series(r, order, options);
 883
 884         // Is the expression of type 0^something?
 885         if (!must_expand_basis && !basis.subs(r, subs_options::no_pattern).is_zero())
 886                 return basic::series(r, order, options);
 887
 888         // Singularity encountered, is the basis equal to (var - point)?
 889         if (basis.is_equal(r.lhs() - r.rhs())) {
 890                 epvector new_seq;
 891                 if (ex_to<numeric>(exponent).to_int() < order)
 892                         new_seq.push_back(expair(_ex1, exponent));
 893                 else
 894                         new_seq.push_back(expair(Order(_ex1), exponent));
 895                 return pseries(r, new_seq);
 896         }
 897
 898         // No, expand basis into series
 899         ex e = basis.series(r, order, options);
 900         return ex_to<pseries>(e).power_const(ex_to<numeric>(exponent), order);
 901 }
 902
 903
 904 /** Re-expansion of a pseries object. */
 905 ex pseries::series(const relational & r, int order, unsigned options) const
 906 {
 907         const ex p = r.rhs();
 908         GINAC_ASSERT(is_a<symbol>(r.lhs()));
 909         const symbol &s = ex_to<symbol>(r.lhs());
 910
 911         if (var.is_equal(s) && point.is_equal(p)) {
 912                 if (order > degree(s))
 913                         return *this;
 914                 else {
 915                         epvector new_seq;
 916                         epvector::const_iterator it = seq.begin(), itend = seq.end();
 917                         while (it != itend) {
 918                                 int o = ex_to<numeric>(it->coeff).to_int();
 919                                 if (o >= order) {
 920                                         new_seq.push_back(expair(Order(_ex1), o));
 921                                         break;
 922                                 }
 923                                 new_seq.push_back(*it);
 924                                 ++it;
 925                         }
 926                         return pseries(r, new_seq);
 927                 }
 928         } else
 929                 return convert_to_poly().series(r, order, options);
 930 }
 931
 932
 933 /** Compute the truncated series expansion of an expression.
 934  *  This function returns an expression containing an object of class pseries
 935  *  to represent the series. If the series does not terminate within the given
 936  *  truncation order, the last term of the series will be an order term.
 937  *
 938  *  @param r  expansion relation, lhs holds variable and rhs holds point
 939  *  @param order  truncation order of series calculations
 940  *  @param options  of class series_options
 941  *  @return an expression holding a pseries object */
 942 ex ex::series(const ex & r, int order, unsigned options) const
 943 {
 944         ex e;
 945         relational rel_;
 946
 947         if (is_a<relational>(r))
 948                 rel_ = ex_to<relational>(r);
 949         else if (is_a<symbol>(r))
 950                 rel_ = relational(r,_ex0);
 951         else
 952                 throw (std::logic_error("ex::series(): expansion point has unknown type"));
 953
 954         try {
 955                 e = bp->series(rel_, order, options);
 956         } catch (std::exception &x) {
 957                 throw (std::logic_error(std::string("unable to compute series (") + x.what() + ")"));
 958         }
 959         return e;
 960 }
 961
 962 } // namespace GiNaC