I think you do not unerstand MATLAB. I'd start with taking the Onramp tutorial. atand of what?
atand is a FUNCTION. You need to pass it arguments. For example, Perhps you intended to write this:
phata_values = atand(phataY./phataX);
Or perhaps you wanted to write
phata_values = atand(z).*(phataY./phataX);
where z is some unknown variable that you never told us about.