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

  
      
      GitHub
  
  
    

pytorch/pytorch 4

pytorch - Tensors and Dynamic neural networks in Python  with strong GPU acceleration