sympy 1.1 : Strange behavior in Matrix.hstack

[Antoine Falaize]

Hello sympy planet!
Is there any reason for the following behavior?

In sympy 1.0:
>>> import sympy as sy

>>> M1 = sy.Matrix.zeros(0, 0)
>>> M2 = sy.Matrix.zeros(0, 1)
>>> M3 = sy.Matrix.zeros(0, 2)
>>> M4 = sy.Matrix.zeros(0, 3)
>>> sy.Matrix.hstack(M1, M2, M3, M4).shape
(0, 6)

But in sympy 1.1:
>>> M1 = sy.Matrix.zeros(0, 0)
>>> M2 = sy.Matrix.zeros(0, 1)
>>> M3 = sy.Matrix.zeros(0, 2)
>>> M4 = sy.Matrix.zeros(0, 3)
>>> sy.Matrix.hstack(M1, M2, M3, M4).shape
(0, 3)

whereas:
>>> M1 = sy.Matrix.zeros(1, 0)
>>> M2 = sy.Matrix.zeros(1, 1)
>>> M3 = sy.Matrix.zeros(1, 2)
>>> M4 = sy.Matrix.zeros(1, 3)
>>> sy.Matrix.hstack(M1, M2, M3, M4).shape
(1, 6)

[Aaron Meurer]

Looks like a bug. Can you open an issue in the issue tracker?

Aaron Meurer

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[Antoine Falaize]

Issue opened here:
https://github.com/sympy/sympy/issues/12938