It depends on what you mean by ‘reciprocal’. If you want ‘X’ such that:
A*X = eye(size(A,1))
X1 = inv(A); % Inverse
X2 = pinv(A); % Pseudo-Inverse
will do what you want.
There are many precautions about calculating the inverse that you will likely encounter. A much better option would be to use the mldivide,\ (link) function if you want to solve linear systems, for example.