Block sparse (#407)

* started implementing block-sparse tensors

* removed files

* working on AbelianIndex

* working in block sparisty

* added reshape

and lots of other stuff

* added Index, an index type for symmetric tensors

* added small tutorial

* added docstring

* fixed bug in retrieve_diagonal_blocks

* TODO added

* improved initialization a bit

* more efficient initialization

* just formatting

* added random

* added fuse_degeneracies

* fixed bug in reshape

* dosctring, typing

* removed TODO

* removed confusing code line

* bug removed

* comment

* added __mul__ to Index

* added sparse_shape

and updated reshape to accept both int and Index lists

* more in tutorial

* comment

* added new test function

* testing function hacking

* docstring

* small speed up

* Remove gui directory (migrated to another repo) (#399)

* a slightly more elegant code

* use one more np function

* removed some crazy slow code

* faster code

* Update README.md (#404)

* add return_data

* doc

* bug fix

Author: mganahl

tensornetwork/block_tensor/block_tensor.py

@@ -576,7 +576,10 @@ def get_diagonal_blocks(self, return_data: Optional[bool] = True) -> Dict:
           "`get_diagonal_blocks` can only be called on a matrix, but found rank={}"
           .format(self.rank))
     return retrieve_non_zero_diagonal_blocks(
-        data=self.data, charges=self.charges, flows=self.flows)
+        data=self.data,
+        charges=self.charges,
+        flows=self.flows,
+        return_data=return_data)
 
 
 def reshape(tensor: BlockSparseTensor,