Schwarz P surface - approximation

Here is an approximation to a Schwarz P surface that I designed for the InforMath project funded by the National Science Foundation (DRL-1323587). The InforMath project (http://informalmathematics.org/) is a partnership between San Diego State University and several museums at the Balboa Park, including the Reuben H. Fleet Science Center (http://www.rhfleet.org/). A Schwarz P surface is a triply periodic minimal surface. The approximation is given by all points (x,y,z) such that cos(x)+cos(y)+c