some more comments and cleanups to mul::expand() and ncmul::expand()
[ginac.git] / ginac / ncmul.cpp
index 7874509e6abecf7f5a03bd4fbe63ef500ffb5328..c4cfe69cb2a93fd3b8afe03f2e571c9a1ba0e34e 100644 (file)
@@ -147,69 +147,69 @@ typedef std::vector<int> intvector;
 
 ex ncmul::expand(unsigned options) const
 {
-       exvector sub_expanded_seq;
-       intvector positions_of_adds;
-       intvector number_of_add_operands;
-
-       exvector expanded_seq=expandchildren(options);
-
-       positions_of_adds.resize(expanded_seq.size());
-       number_of_add_operands.resize(expanded_seq.size());
-
-       int number_of_adds=0;
-       int number_of_expanded_terms=1;
-
-       unsigned current_position=0;
-       exvector::const_iterator last=expanded_seq.end();
+       // First, expand the children
+       exvector expanded_seq = expandchildren(options);
+
+       // Now, look for all the factors that are sums and remember their
+       // position and number of terms. One remark is in order here: we do not
+       // take into account the overall_coeff of the add objects. This is
+       // because in GiNaC, all terms of a sum must be of the same type, so
+       // a non-zero overall_coeff (which can only be numeric) would imply that
+       // the sum only has commutative terms. But then it would never appear
+       // as a factor of an ncmul.
+       intvector positions_of_adds(expanded_seq.size());
+       intvector number_of_add_operands(expanded_seq.size());
+
+       int number_of_adds = 0;
+       int number_of_expanded_terms = 1;
+
+       unsigned current_position = 0;
+       exvector::const_iterator last = expanded_seq.end();
        for (exvector::const_iterator cit=expanded_seq.begin(); cit!=last; ++cit) {
-               if (is_ex_exactly_of_type((*cit),add)) {
-                       positions_of_adds[number_of_adds]=current_position;
-                       const add & expanded_addref=ex_to<add>(*cit);
-                       number_of_add_operands[number_of_adds]=expanded_addref.seq.size();
+               if (is_ex_exactly_of_type(*cit, add)) {
+                       positions_of_adds[number_of_adds] = current_position;
+                       const add & expanded_addref = ex_to<add>(*cit);
+                       number_of_add_operands[number_of_adds] = expanded_addref.seq.size();
                        number_of_expanded_terms *= expanded_addref.seq.size();
                        number_of_adds++;
                }
                current_position++;
        }
 
-       if (number_of_adds==0) {
-               return (new ncmul(expanded_seq,1))->setflag(status_flags::dynallocated ||
-                                                                                                       status_flags::expanded);
-       }
+       // If there are no sums, we are done
+       if (number_of_adds == 0)
+               return (new ncmul(expanded_seq, true))->
+                       setflag(status_flags::dynallocated | (options == 0 ? status_flags::expanded : 0));
 
+       // Now, form all possible products of the terms of the sums with the
+       // remaining factors, and add them together
        exvector distrseq;
        distrseq.reserve(number_of_expanded_terms);
 
-       intvector k;
-       k.resize(number_of_adds);
-       
-       int l;
-       for (l=0; l<number_of_adds; l++) {
-               k[l]=0;
-       }
+       intvector k(number_of_adds);
 
-       while (1) {
-               exvector term;
-               term=expanded_seq;
-               for (l=0; l<number_of_adds; l++) {
-                       GINAC_ASSERT(is_ex_exactly_of_type(expanded_seq[positions_of_adds[l]],add));
-                       const add & addref=ex_to<add>(expanded_seq[positions_of_adds[l]]);
-                       term[positions_of_adds[l]]=addref.recombine_pair_to_ex(addref.seq[k[l]]);
+       while (true) {
+               exvector term = expanded_seq;
+               for (int i=0; i<number_of_adds; i++) {
+                       GINAC_ASSERT(is_ex_exactly_of_type(expanded_seq[positions_of_adds[i]], add));
+                       const add & addref = ex_to<add>(expanded_seq[positions_of_adds[i]]);
+                       term[positions_of_adds[i]] = addref.recombine_pair_to_ex(addref.seq[k[i]]);
                }
-               distrseq.push_back((new ncmul(term,1))->setflag(status_flags::dynallocated |
-                                                                                                               status_flags::expanded));
+               distrseq.push_back((new ncmul(term, true))->
+                                   setflag(status_flags::dynallocated | (options == 0 ? status_flags::expanded : 0)));
 
                // increment k[]
-               l=number_of_adds-1;
-               while ((l>=0)&&((++k[l])>=number_of_add_operands[l])) {
-                       k[l]=0;    
+               int l = number_of_adds-1;
+               while ((l>=0) && ((++k[l]) >= number_of_add_operands[l])) {
+                       k[l] = 0;
                        l--;
                }
-               if (l<0) break;
+               if (l<0)
+                       break;
        }
 
-       return (new add(distrseq))->setflag(status_flags::dynallocated |
-                                                                               status_flags::expanded);
+       return (new add(distrseq))->
+               setflag(status_flags::dynallocated | (options == 0 ? status_flags::expanded : 0));
 }
 
 int ncmul::degree(const ex & s) const