- power::eval(): for the case (b_n/b_d)^(e_n/e_d) we now check separately
authorRichard Kreckel <Richard.Kreckel@uni-mainz.de>
Fri, 27 Jul 2001 03:58:21 +0000 (03:58 +0000)
committerRichard Kreckel <Richard.Kreckel@uni-mainz.de>
Fri, 27 Jul 2001 03:58:21 +0000 (03:58 +0000)
  if we can compute numerator and denominator.  This allows us to eval
  (3/8)^(1/3) to 1/2*3^(1/3) instead of holding it.  For square roots this
  is still less clever than what MapleV does, but then again that system
  has the funny goof not to touch 8^(1/3) where we immediately eval() to
  plain 2; fun, fun, fun...
  Oh, and a little memory hole has been squished along the way, too.

ginac/power.cpp

index 2d4360dea0cce94416d4f136872a2c5d7da9561e..3400e6aa0cfeba2757e0c1a8cef9e0f1f0f8d1b4 100644 (file)
@@ -317,16 +317,16 @@ ex power::eval(int level) const
        
        bool basis_is_numerical = false;
        bool exponent_is_numerical = false;
        
        bool basis_is_numerical = false;
        bool exponent_is_numerical = false;
-       numeric * num_basis;
-       numeric * num_exponent;
+       const numeric *num_basis;
+       const numeric *num_exponent;
        
        if (is_exactly_of_type(*ebasis.bp,numeric)) {
                basis_is_numerical = true;
        
        if (is_exactly_of_type(*ebasis.bp,numeric)) {
                basis_is_numerical = true;
-               num_basis = static_cast<numeric *>(ebasis.bp);
+               num_basis = static_cast<const numeric *>(ebasis.bp);
        }
        if (is_exactly_of_type(*eexponent.bp,numeric)) {
                exponent_is_numerical = true;
        }
        if (is_exactly_of_type(*eexponent.bp,numeric)) {
                exponent_is_numerical = true;
-               num_exponent = static_cast<numeric *>(eexponent.bp);
+               num_exponent = static_cast<const numeric *>(eexponent.bp);
        }
        
        // ^(x,0) -> 1 (0^0 also handled here)
        }
        
        // ^(x,0) -> 1 (0^0 also handled here)
@@ -340,7 +340,7 @@ ex power::eval(int level) const
        // ^(x,1) -> x
        if (eexponent.is_equal(_ex1()))
                return ebasis;
        // ^(x,1) -> x
        if (eexponent.is_equal(_ex1()))
                return ebasis;
-       
+
        // ^(0,c1) -> 0 or exception (depending on real value of c1)
        if (ebasis.is_zero() && exponent_is_numerical) {
                if ((num_exponent->real()).is_zero())
        // ^(0,c1) -> 0 or exception (depending on real value of c1)
        if (ebasis.is_zero() && exponent_is_numerical) {
                if ((num_exponent->real()).is_zero())
@@ -350,44 +350,64 @@ ex power::eval(int level) const
                else
                        return _ex0();
        }
                else
                        return _ex0();
        }
-       
+
        // ^(1,x) -> 1
        if (ebasis.is_equal(_ex1()))
                return _ex1();
        // ^(1,x) -> 1
        if (ebasis.is_equal(_ex1()))
                return _ex1();
-       
+
        if (exponent_is_numerical) {
 
                // ^(c1,c2) -> c1^c2 (c1, c2 numeric(),
                // except if c1,c2 are rational, but c1^c2 is not)
                if (basis_is_numerical) {
        if (exponent_is_numerical) {
 
                // ^(c1,c2) -> c1^c2 (c1, c2 numeric(),
                // except if c1,c2 are rational, but c1^c2 is not)
                if (basis_is_numerical) {
-                       bool basis_is_crational = num_basis->is_crational();
-                       bool exponent_is_crational = num_exponent->is_crational();
-                       numeric res = num_basis->power(*num_exponent);
-               
-                       if ((!basis_is_crational || !exponent_is_crational)
-                               || res.is_crational()) {
+                       const bool basis_is_crational = num_basis->is_crational();
+                       const bool exponent_is_crational = num_exponent->is_crational();
+                       if (!basis_is_crational || !exponent_is_crational) {
+                               // return a plain float
+                               return (new numeric(num_basis->power(*num_exponent)))->setflag(status_flags::dynallocated |
+                                                                                              status_flags::evaluated |
+                                                                                              status_flags::expanded);
+                       }
+
+                       const numeric res = num_basis->power(*num_exponent);
+                       if (res.is_crational()) {
                                return res;
                        }
                        GINAC_ASSERT(!num_exponent->is_integer());  // has been handled by now
 
                                return res;
                        }
                        GINAC_ASSERT(!num_exponent->is_integer());  // has been handled by now
 
-                       // ^(c1,n/m) -> *(c1^q,c1^(n/m-q)), 0<(n/m-h)<1, q integer
+                       // ^(c1,n/m) -> *(c1^q,c1^(n/m-q)), 0<(n/m-q)<1, q integer
                        if (basis_is_crational && exponent_is_crational
                        if (basis_is_crational && exponent_is_crational
-                               && num_exponent->is_real()
-                               && !num_exponent->is_integer()) {
-                               numeric n = num_exponent->numer();
-                               numeric m = num_exponent->denom();
+                           && num_exponent->is_real()
+                           && !num_exponent->is_integer()) {
+                               const numeric n = num_exponent->numer();
+                               const numeric m = num_exponent->denom();
                                numeric r;
                                numeric q = iquo(n, m, r);
                                if (r.is_negative()) {
                                numeric r;
                                numeric q = iquo(n, m, r);
                                if (r.is_negative()) {
-                                       r = r.add(m);
-                                       q = q.sub(_num1());
+                                       r += m;
+                                       --q;
                                }
                                }
-                               if (q.is_zero())  // the exponent was in the allowed range 0<(n/m)<1
+                               if (q.is_zero()) {  // the exponent was in the allowed range 0<(n/m)<1
+                                       if (num_basis->is_rational() && !num_basis->is_integer()) {
+                                               // try it for numerator and denominator separately, in order to
+                                               // partially simplify things like (5/8)^(1/3) -> 1/2*5^(1/3)
+                                               const numeric bnum = num_basis->numer();
+                                               const numeric bden = num_basis->denom();
+                                               const numeric res_bnum = bnum.power(*num_exponent);
+                                               const numeric res_bden = bden.power(*num_exponent);
+                                               if (res_bnum.is_integer())
+                                                       return (new mul(power(bden,-*num_exponent),res_bnum))->setflag(status_flags::dynallocated | status_flags::evaluated);
+                                               if (res_bden.is_integer())
+                                                       return (new mul(power(bnum,*num_exponent),res_bden.inverse()))->setflag(status_flags::dynallocated | status_flags::evaluated);
+                                       }
                                        return this->hold();
                                        return this->hold();
-                               else {
-                                       epvector res;
-                                       res.push_back(expair(ebasis,r.div(m)));
-                                       return (new mul(res,ex(num_basis->power_dyn(q))))->setflag(status_flags::dynallocated | status_flags::evaluated);
+                               } else {
+                                       // assemble resulting product, but allowing for a re-evaluation,
+                                       // because otherwise we'll end up with something like
+                                       //    (7/8)^(4/3)  ->  7/8*(1/2*7^(1/3))
+                                       // instead of 7/16*7^(1/3).
+                                       ex prod = power(*num_basis,r.div(m));
+                                       return prod*power(*num_basis,q);
                                }
                        }
                }
                                }
                        }
                }
@@ -421,7 +441,7 @@ ex power::eval(int level) const
                                const numeric & num_coeff = ex_to<numeric>(mulref.overall_coeff);
                                if (num_coeff.is_real()) {
                                        if (num_coeff.is_positive()) {
                                const numeric & num_coeff = ex_to<numeric>(mulref.overall_coeff);
                                if (num_coeff.is_real()) {
                                        if (num_coeff.is_positive()) {
-                                               mul * mulp = new mul(mulref);
+                                               mul *mulp = new mul(mulref);
                                                mulp->overall_coeff = _ex1();
                                                mulp->clearflag(status_flags::evaluated);
                                                mulp->clearflag(status_flags::hash_calculated);
                                                mulp->overall_coeff = _ex1();
                                                mulp->clearflag(status_flags::evaluated);
                                                mulp->clearflag(status_flags::hash_calculated);
@@ -430,7 +450,7 @@ ex power::eval(int level) const
                                        } else {
                                                GINAC_ASSERT(num_coeff.compare(_num0())<0);
                                                if (num_coeff.compare(_num_1())!=0) {
                                        } else {
                                                GINAC_ASSERT(num_coeff.compare(_num0())<0);
                                                if (num_coeff.compare(_num_1())!=0) {
-                                                       mul * mulp = new mul(mulref);
+                                                       mul *mulp = new mul(mulref);
                                                        mulp->overall_coeff = _ex_1();
                                                        mulp->clearflag(status_flags::evaluated);
                                                        mulp->clearflag(status_flags::hash_calculated);
                                                        mulp->overall_coeff = _ex_1();
                                                        mulp->clearflag(status_flags::evaluated);
                                                        mulp->clearflag(status_flags::hash_calculated);
@@ -451,17 +471,17 @@ ex power::eval(int level) const
        }
        
        if (are_ex_trivially_equal(ebasis,basis) &&
        }
        
        if (are_ex_trivially_equal(ebasis,basis) &&
-               are_ex_trivially_equal(eexponent,exponent)) {
+           are_ex_trivially_equal(eexponent,exponent)) {
                return this->hold();
        }
        return (new power(ebasis, eexponent))->setflag(status_flags::dynallocated |
                return this->hold();
        }
        return (new power(ebasis, eexponent))->setflag(status_flags::dynallocated |
-                                                                                                  status_flags::evaluated);
+                                                      status_flags::evaluated);
 }
 
 ex power::evalf(int level) const
 {
        debugmsg("power evalf",LOGLEVEL_MEMBER_FUNCTION);
 }
 
 ex power::evalf(int level) const
 {
        debugmsg("power evalf",LOGLEVEL_MEMBER_FUNCTION);
-
+       
        ex ebasis;
        ex eexponent;
        
        ex ebasis;
        ex eexponent;
        
@@ -558,8 +578,8 @@ ex power::expand(unsigned options) const
        if (options == 0 && (flags & status_flags::expanded))
                return *this;
        
        if (options == 0 && (flags & status_flags::expanded))
                return *this;
        
-       ex expanded_basis = basis.expand(options);
-       ex expanded_exponent = exponent.expand(options);
+       const ex expanded_basis = basis.expand(options);
+       const ex expanded_exponent = exponent.expand(options);
        
        // x^(a+b) -> x^a * x^b
        if (is_ex_exactly_of_type(expanded_exponent, add)) {
        
        // x^(a+b) -> x^a * x^b
        if (is_ex_exactly_of_type(expanded_exponent, add)) {