From 26ed939901fab6d2f28b4feeb8f865345713ed19 Mon Sep 17 00:00:00 2001
From: Jiri Pittner <jiri@pittnerovi.com>
Date: Mon, 15 Dec 2025 20:32:01 +0100
Subject: [PATCH] tensor: bugfix in unwind_index and linear_transform of single
 group

---
 t.cc      | 52 ++++++++++++++++++++++++++++++++++++++++++-
 tensor.cc | 66 ++++++++++++++++++++++++++++++++++++++++++++++++++++++-
 tensor.h  |  2 ++
 3 files changed, 118 insertions(+), 2 deletions(-)

diff --git a/t.cc b/t.cc
index afbfa31..b27c65a 100644
--- a/t.cc
+++ b/t.cc
@@ -4534,7 +4534,7 @@ for(int i=0; i<m; ++i)
 
 }
 
-if(1)
+if(0)
 {
 int n,m;
 bool which;
@@ -4570,6 +4570,56 @@ for(int i=0; i<m; ++i)
 	cout <<endl;
 	}
 
+}
+
+if(1)
+{
+int r,n,sym;
+cin>>r>>n>>sym;
+NRVec<INDEXGROUP> shape(3);
+	shape[0].number=2; 
+        shape[0].symmetry=0;
+        shape[0].range=n+1;
+        shape[0].offset=0;
+
+        shape[1].number=r;
+        shape[1].symmetry= sym;
+        shape[1].range=n;
+        shape[1].offset=0;
+
+        shape[2].number=2;
+        shape[2].symmetry=0;
+        shape[2].range=n+2;
+        shape[2].offset=0;
+
+
+Tensor<double> x(shape); x.randomize(1.);
+x.defaultnames();
+cout <<"x= "<<x.shape << " "<<x.names<<endl;
+
+NRVec<INDEXGROUP> yshape(2);
+        yshape[0].number=1; 
+        yshape[0].symmetry=0;
+        yshape[0].range=n;
+        yshape[0].offset=0;
+        
+        yshape[1].number=1; 
+        yshape[1].symmetry= 0;
+        yshape[1].range=n+3;
+        yshape[1].offset=0;
+
+Tensor<double> y(yshape); y.randomize(1.);
+
+INDEX posit(1,0);
+//Tensor<double> z=x.unwind_index(1,1);
+//Tensor<double> z=x.contraction(INDEX(1,1),y,INDEX(0,0),1,false,false);
+Tensor<double> z=x.linear_transform(1,y);
+
+cout <<z.shape;
+
+//check
+
+
 }
 
 }//main
diff --git a/tensor.cc b/tensor.cc
index 88fb736..c2704df 100644
--- a/tensor.cc
+++ b/tensor.cc
@@ -713,6 +713,9 @@ return q;
 template<typename T>
 Tensor<T> Tensor<T>::permute_index_groups(const NRPerm<int> &p) const
 {
+if(p.size()!=shape.size()) laerror("permutation size mismatch in permute_index_groups");
+if(p.is_identity()) return *this;
+
 //std::cout <<"permute_index_groups permutation = "<<p<<std::endl;
 NRVec<INDEXGROUP> newshape=shape.permuted(p,true);
 //std::cout <<"permute_index_groups newshape = "<<newshape<<std::endl;
@@ -836,6 +839,7 @@ if(group==0 && index==0 && shape[0].symmetry==0) //formal split of 1 index witho
 	}
 if(shape[group].number==1) return unwind_index_group(group); //single index in the group
 
+
 //general case - recalculate the shape and allocate the new tensor
 NRVec<INDEXGROUP> newshape(shape.size()+1);
 newshape[0].number=1;
@@ -856,7 +860,10 @@ for(int i=0; i<shape.size(); ++i)
 		--newshape[i+1].number;
 		flatindex += index;
 		}
-	else flatindex += shape[i].number;
+	else 
+		{
+		if(i<group) flatindex += shape[i].number;
+		}
 	}
 
 
@@ -1840,6 +1847,10 @@ for(int g=shape.size()-1; g>=0; --g)
 	Tensor<T> mat(x[g],true); //flat tensor from a matrix
 	for(int i=shape[g].number-1; i>=0; --i) //indices in the group in reverse order
 		{
+#ifdef LA_TENSOR_INDEXPOSITION
+		//what should we do with index position?
+		//either set upperindex of mat appropriately, or request ignoring that in contractions?
+#endif
 		r= tmp.contraction(indexposition(rank()-1,tmp.shape),mat,INDEX(0,0),(T)1,false,false); //always the last index
 		if(i>0)
                 	{
@@ -1870,6 +1881,59 @@ return r;
 }
 
 
+template<typename T>
+Tensor<T> Tensor<T>::linear_transform(const int g, const Tensor<T> &x) const
+{
+if(g<0||g>=shape.size()) laerror("wrong index group number in linear_transform");
+if(x.rank()!=2 || x.shape.size()!=2 || x.shape[0].number!=1||x.shape[1].number!=1) laerror("wrong tensor shape for linear_transform");
+if(x.shape[0].range!=shape[g].range) laerror("index range mismatch in linear_transform");
+
+Tensor<T> tmp(*this);
+Tensor<T> r;
+
+
+//contract all indices in the reverse order
+	int gnow=g;
+	for(int i=shape[g].number-1; i>=0; --i) //indices in the group in reverse order
+		{
+		r= tmp.contraction(INDEX(gnow,i),x,INDEX(0,0),(T)1,false,false);
+		++gnow; //new group number in r, one index was added left
+		if(i>0)
+                	{
+                	tmp=r;
+                	r.deallocate();
+			}
+		}
+//the group's indices are now individual ones leftmost in tensor r, restore group size and symmetry
+	if(shape[g].number>1)
+		{
+		INDEXLIST il(shape[g].number);
+		for(int i=0; i<shape[g].number; ++i)
+			{
+			il[i].group=i;
+			il[i].index=0;
+			}
+		r = r.merge_indices(il,shape[g].symmetry);
+		}
+
+//permute the group (now 0) to its original position
+if(g!=0)
+	{
+	NRPerm<int> p(r.shape.size());
+	for(int i=0; i<g; ++i) p[i+1] = (i+1)+1;
+	p[g+1]=1;
+	for(int i=g+1; i<r.shape.size();++i) p[i+1] = i+1;
+	//std::cout<<"perm "<<p;
+	r=r.permute_index_groups(p);
+	}
+
+//preserve names
+r.names=names;
+
+return r;
+}
+
+
 
 template<typename T> 
 int Tensor<T>::findflatindex(const INDEXNAME nam) const
diff --git a/tensor.h b/tensor.h
index 7b6d379..c4bbc35 100644
--- a/tensor.h
+++ b/tensor.h
@@ -421,6 +421,8 @@ public:
 	NRVec<NRMat<T> > Tucker(typename LA_traits<T>::normtype thr=1e-12, bool inverseorder=false); //HOSVD-Tucker decomposition, return core tensor in *this, flattened 
 	Tensor inverseTucker(const NRVec<NRMat<T> > &x, bool inverseorder=false) const; //rebuild the original tensor from Tucker
 	Tensor linear_transform(const NRVec<NRMat<T> > &x) const; //linear transform by a different matrix per each index group, preserving group symmetries
+	Tensor linear_transform(const int g, const Tensor<T> &x) const; //linear transform a single group, preserve its position and symmetry, x must be rank-2 flat tensor (this is useful for raising/lowering indices)
+	Tensor linear_transform(const int g, const NRMat<T> &x) const {Tensor<T> mat(x,true); return linear_transform(g,mat);}; //linear transform a single group, preserve its position and symmetry
 };