Unused code/syntax error in matexpr

[oscargus]

It seems like the following code will not work (and therefore is probably not tested). Subject to something really clever that I cannot figure out:

sympy/sympy/matrices/expressions/matexpr.py

Lines 931 to 942 in 97d5a89

	if _get_shape(self.first)[1] != _get_shape(self.second)[1]:
	# Remove one-dimensional identity matrices:
	# (this is needed by `a.diff(a)` where `a` is a vector)
	if _get_shape(self.second) == (1, 1):
	return self.first*self.second[0, 0]
	if _get_shape(self.first) == (1, 1):
	return self.first[1, 1]*self.second.T
	raise ValueError("incompatible shapes")
	if self.first != 1:
	return self.first*self.second.T
	else:
	return self.higher

Especially, self.first and self.second is not defined. Should it be self.first_pointer and self.second_pointer?

@Upabjojr

[Upabjojr]

That is part of the matrix derivation algorithm. It might be that it's a bit defective. I plan to eventually replace it with a new algorithm in the module sympy.tensor.array.expressions, which as of now is not complete. As soon as the new module is finished, most stuff related to matrix derivations in sympy.matrices.expressions will be removed (like the _LeftRightArgs class).

I wouldn't concentrate on fixing the _LeftRightArgs class, as it will hopefully be fully removed in the future.