Update tenmat to updated constructor interface

[ntjohnson1]

Follow up to

• 145

• 213

Follow changes from #182 for ktensor as a guide.

Constructors:

• Update: __init__: (replaces from_data, adds copy parameter)
• Remove: from_tensor_type
• Remove: from_data

Add methods:

• copy
• __deepcopy__

[ntjohnson1]

Additional topics to cover from the tutorials:

Converting a Tensor to a Matrix and Vice Versa

• [ ] Documentation: descriptive documentation of ttb.tenmat.from_tensor_type()
• [ ] Suggestion: include definition of matriculation from Kolda & Bader (Sec. 2.4)
• [ ] Explicitly define cdims_cyclic

  Creating a tenmat (tensor as matrix) object

• [ ] It would be helpful to see a full description upfront of the optional arguments rdims, cdims, and cdims_cyclic (they are not defined when calling help(ttb.tenmat.from_tensor_type)
• [ ] Use rdims=, cdims=, and cdims_cyclic= more aggressively

[ntjohnson1]

We want to update sptenmat similarly to match

[ntjohnson1]

Right now our tenmat construction is a little bit of a mess. I suspect we are hitting some weirdness related to fortran layouts again. from_data actually creates a tensor then calls from_tensor as our base case. This is needed because from_tensor actually reshapes the matrix into the original tensor size then reflattens it which seems like it shouldn't be necessary (but we get a variety of failures if we skip that step).

[ntjohnson1]

Ok. I figured out the decoupling. Currently from_data increased the scope from Matlab to accept any data that could be coerced into the correct shape instead of a matrix that can be unwrapped into a tensor. I should hopefully have a cleaned up version in the next few days.