tensor: permute index group to a given index order

t.cc

@@ -4120,7 +4120,7 @@ Tensor<double> ss(s);
 cout <<"Error= "<<ss-xc<<endl;
 }
 
-if(1)
+if(0)
 {
 int r=1;
 int n=5;
@@ -4140,6 +4140,29 @@ cout <<x*s1<<endl;
 cout<<s1*s2<<endl;
 }
 
+if(1)
+{
+int r;
+int n;
+cin>>r>>n;
+NRVec<INDEXGROUP> s(r);
+for(int i=0; i<r; ++i)
+        {
+        s[i].number=1;
+        s[i].symmetry=0;
+        s[i].range=n;
+        s[i].offset=0;
+        }
+Tensor<double> x(s); x.randomize(1.);
+x.defaultnames();
+NRVec<INDEXNAME> names(r);
+NRPerm<int> p(r); p.randomize();
+for(int i=0; i<r; ++i) sprintf(names[i].name,"i%03d",p[i+1]-1);
+cout <<"requested index order = "<<names<<endl;
+Tensor<double> y = x.permute_index_groups(names);
+cout<<"resulting index order = "<<y.names<<endl;
+}
+
 
 
 }//main

tensor.cc

@@ -705,6 +705,23 @@ return r;
 }
 
 
+template<typename T>
+Tensor<T> Tensor<T>::permute_index_groups(const NRVec<INDEXNAME> &names) const
+{
+NRPerm<int> p(shape.size());
+if(names.size()!=shape.size()) laerror("names list does not match shape in permute_index_groups");
+for(int i=0; i<names.size(); ++i)
+	{
+	INDEX ii=findindex(names[i]);
+	if(ii.index>0) laerror("indices inside groups cannot be permuted in permute_index_groups, define permutation by first group's index name or flatten the tensor first");
+	p[1+i] = 1+ii.group;
+	}
+if(!p.is_valid()) laerror("illegal permutation from names in permute_index_groups, perhaps repeated or not unique names?");
+return permute_index_groups(p);
+}
+
+
+
 FLATINDEX superindex2flat(const SUPERINDEX &I)
 {
 int rank=0;

tensor.h

@@ -40,8 +40,6 @@
 #include "miscfunc.h"
 
 //TODO:
-//@@@?general permutation of individual indices - check the indices in sym groups remain adjacent, calculate result's shape, loopover the result and permute using unwind_callback
-//@@@ is that needed? we can flatten the relevant groups and permute index groups alternatively - maybe implement on high level this way for convenience
 //?maybe optional negative range for beta spin handling in some cases of fourindex-tensor conversions combining AA and AB etc. cases - if needed
 
 
@@ -299,7 +297,8 @@ public:
 	void grouploopover(void (*callback)(const GROUPINDEX &, T *)); //loop over all elements disregarding the internal structure of index groups
 	void constgrouploopover(void (*callback)(const GROUPINDEX &, const T *)) const; //loop over all elements disregarding the internal structure of index groups
 
-	Tensor permute_index_groups(const NRPerm<int> &p) const; //rearrange the tensor storage permuting index groups as a whole
+	Tensor permute_index_groups(const NRPerm<int> &p) const; //rearrange the tensor storage permuting index groups as a whole: result_i = source_p_i
+	Tensor permute_index_groups(const NRVec<INDEXNAME> &names) const; //permute to requested order of group's first indices (or permute individual indices of a flat tensor)
 
 	Tensor unwind_index_group(int group) const; //make the index group leftmost (least significant)
 	Tensor unwind_index(int group, int index) const; //separate an index from a group and expand it to full range as the least significant one (the leftmost one)