Matrix and _eval_diff

[Francesco Bonazzi]

Is there a reason why matrices don't implement _eval_diff?

Elementwise derivatives are currently handled by the diff method.

Calling matrix.diff(x) calculates derivatives elementwisely, diff(matrix, x) returns an unevaluated derivative.

In [12]: var('x y z')
Out[12]: (x, y, z)

In [13]: m = Matrix([[x, y], [x*y, x*z]])

In [14]: m.diff(x)
Out[14]:
Matrix([
[1, 0],
[y, z]])

In [15]: diff(m, x)
Out[15]:
Derivative(Matrix([
[  x,   y],
[x*y, x*z]]), x)

[Aaron Meurer]

I guess because mutable matrices aren't subclasses of Expr, they need
to implement diff. I don't think there is a specific reason _eval_diff
is missing. It probably was never implemented.

Aaron Meurer

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[Francesco Bonazzi]

On Saturday, 2 January 2016 23:19:13 UTC+1, Aaron Meurer wrote:

I don't think there is a specific reason _eval_diff
is missing. It probably was never implemented.

Here we go: https://github.com/sympy/sympy/pull/10490