Conda has three version for cuda91 that you can get:
$conda install -c pytorch cuda91
$conda install -c soumith cuda91
$conda install -c soumith magma-cuda91
Is there relevant different between them? the Github documents point to magma-cuda80
I think you should install the magma-cudaxx with xx corresponding to the cuda version you have installed.
If you don’t have any, use the latest (9.1 at time of writing).