Always use array in lambdify

[asmeurer]

See #2987 (comment) and #2931. We should just always use array, and print matrix multiplication as np.dot. We should revert the change from #2987. If you really want to use np.matrix, you can use the namespace option of lambdify.

This should be done before the next release, at least the reversion of #2987 so that we don't add a new API that will then be removed.

[jcrist]

I'm currently working on this. As expressions are evaluated before lambdify uses them, matrix multiplication in a lambda expression doesn't seem to occur (the return is a matrix/array). The only time I can think of that matrix multiplication may be used would be if someone tried to lambdify an expression using MatrixSymbol. Trying this on version 0.75 errors out due to a bad lambda representation of MatrixSymbol. Should this feature be added?

[asmeurer]

Or MatMul, even with an ImmutableMatrix.

[asmeurer]

As it remains unevaluated by default.

[jcrist]

The only way I can seem to manage to generate a MatMul expression is with multiplication between a MatrixSymbol, and something else. Multiplying two ImmutableMatrix objects evaluates, rather than returning a MatMul (unless that's not what you're saying).

[asmeurer]

In [6]: MatMul(Matrix([[1, 2], [3, 4]]), Matrix([1, 2]))
Out[6]:
⎡1  2⎤⋅⎡1⎤
⎢    ⎥ ⎢ ⎥
⎣3  4⎦ ⎣2⎦

This will also happen if you replace a MatrixSymbol with an actual matrix in an expression (see #2962)

[jcrist]

Hmmm. Didn't realize you could create a MatMul object directly. The fix proposed in PR 7293 still fixes this issue though. Works for any MatMul object.

[jcrist]

Silly github, closing issues automatically just because people mention them in pull requests. The first part of this is fixed (removal of kwarg, use numpy.array). The second part (printing array using numpy.dot for all MatrixExpr types) still needs to be done.

[jcrist]

I think this can be deferred until later. It's at least no longer critical, as the array portion is taken care of. Appropriately handling matrix operations requires more changes than I have I have time to implement right now.

I'm deferring this to 0.7.7, and removing the critical status.

[asmeurer]

0.7.7, now 1.0, is coming up. What needs to be done here?

[asmeurer]

See #7853 and #9191.