Matrix expressions

[rikardn]

A start for Matrix expressions

• IdentityMatrix
• ZeroMatrix
• DiagonalMatrix (immutable special case matrix literal)
• MatrixAdd

Test functions for matrix expressions:

• is_zero
• is_real
• is_symmetric
• is_square
• is_diagonal
• is_lower
• is_upper
• is_toeplitz

[rikardn]

Also added:

• HadamardProduct
• MatrixSymbol
• ImmutableDenseMatrix (dense matrix that is derived from Basic and MatrixExpr)

[rikardn]

This is ready for review. I apologise for the massive PR. I don't think the error is related to this PR, but not sure. Any thoughts on that would be appreciated.

[isuruf]

Can you combine the headers is_foo.h into one header? There's really no reason to have a header with just one function in it.

Also, I'm not a fan of adding one file per function is_foo.cpp. This would increase the compilation time significantly, though it increases the readability too.

[rikardn]

Moved declarations of all is_ functions to matrix_expressions.h. On the cpp file side I find things much easier to find and read with one file per class or function implementation. Let me know @isuruf if you don't think it is ok.

[rikardn]

Can this be merged?

[rikardn]

I finally got this rebased and through the tests. I'll merge now and further work can go into new PRs. Thanks @isuruf for reviewing.