Substituting MatrixSymbol in Matrix only changes first component

[nschloe]

When substituting a MatrixSymbol in a Matrix, only the first Matrix component is changed.

MVCE:

import sympy

a = sympy.MatrixSymbol('a', 2, 1)

A = sympy.Matrix([[a[0], a[1]**2]])                                             

a_vals = [1.0, 2.0]
print(A.subs(zip(a, a_vals)))

Output:

Matrix([[1.00000000000000, a[1, 0]**2]])

Expected output:

Matrix([[1.00000000000000, 4.00000000000000]])

[normalhuman]

It seems the conversion to dict, from our mailing list discussion, is needed sometimes.

>>> print(A.subs(dict(zip(a, a_vals))))
Matrix([[1.00000000000000, 4.00000000000000]])

Same for a tuple or list of tuples.

>>> print(A.subs(tuple(zip(a, a_vals))))
Matrix([[1.00000000000000, 4.00000000000000]])
>>> print(A.subs(list(zip(a, a_vals))))
Matrix([[1.00000000000000, 4.00000000000000]])

But I see no reason why passing an iterator to subs shouldn't work in this specific setup, so looks like a bug.

[ethankward]

See also #13330