Question about correlation of two signals I'm working on some practice examples and in one of them I'm asked to find the convolution and the correlation of some signal pairs given. I know that correlation , given two signals x(n),g(n), is given by the following :
$$Φ_{xg}=x(n)\ast g(-n)$$ where asterisk is convolution. Now is this the same as $$g(n)\ast x(-n)$$ 

I think I read this somewhere $$Φ_{xy}(n)=Φ_{yx}(-n)$$ So the 2 convolutions give different results. Shouldn't the question specify which correlation I am to calculate? $$Φ_{xy}\\Φ_{yx}$$
You are correct in noting that cross-correlation is not commutative. If the question says "correlation between two signals $x$ and $g$" then it is usually assumed that you go in that sequence and compute $\Phi_{xg}$. 

Or you can choose to say that the question and ambiguous compute both $\Phi_{xg}$ and $\Phi_{gx}.$