Hello.

I am studying the tensor renormalzation group.

In the renormalization step, I use SVD to obtain a truncated matrices.

```
auto A = replaceTags(replaceTags(R_L,"x2","x1"),"x4","x3")*R_R;
auto [U, S, V] = svd(A, {ind_RL},{"MaxDim",dxn,"LeftTags","ulink","RightTags","vlink"});
```

Problem is, when I run the code with a 6400 x 6400 matrix A, SVD takes about 1000 seconds.

When I run SVD with mkl LAPACKE_zgesvd with the same matrix, it takes about 75 seconds.

( This process includes storing the tensor A to 1D array and assigning the output elements of [U, S, V] to the ITensor container after the SVD operation.)

I am wondering why this happened. I thought running ITensor SVD and mkl LAPACK routine should take the same time...

Thanks.

Best,

hexagon