You wrote
psi(i,j) = ((U0*V0)./W)*cos(W(t-YY(i,j)./V0))-V0*XX(i,j);
Try
psi(i,j) = ((U0*V0)./W)*cos(W*(t-YY(i,j)./V0))-V0*XX(i,j);
W is not a vector or matrix, so calling W(t-YY(i,j)./V0) won't return anything sensible. I think you mean to multiply W by the bracketed term in the cos.
Side note: i and j make terrible variable names in Matlab. They already have a built in value of the complex unit, so redefining that is likely to throw errors further down the line. I tend to use ii, jj or k for loop indices to avoid this problem.
