Well, yes, you've tried to compare the LHS to the RHS via the equality "==" operator for some reason that is not at all clear although the immediate error is owing to the fact that neither variable referenced on the LHS is defined.
We don't know what you expect the function to do or return -- there's quite a lot wrong here besides beginning with the minor detail that equation is missspelled altho MATLAB doesn't care, it'll cause difficulty in remembering to use the misspellled version if continue.
But, you pass arguments x,y into the function but immediately overwrite them with local variables -- whassup w/ that?
There's really no way to proceed from this -- tell us what you're trying to do and include a sample of inputs and expected output(s) to help with the explanation.
