code: def spher_to_cyl(r, theta, phi):
      
      R = r*nu.sin(theta)
      z = r*nu.cos(theta)
      return (R,z, phi)
docs: NAME:
  
         spher_to_cyl
  
      PURPOSE:
  
         convert from spherical to cylindrical coordinates
  
      INPUT:
  
         r, theta, phi - spherical coordinates
  
      OUTPUT:
  
         R, z, phi - spherical coordinates
  
      HISTORY:
  
         2016-05-20 - Written - Aladdin