def to_struct_file(self, f):
        """ write the Vario2d to a PEST-style structure file

        Parameters
        ----------
        f : (str or file handle)
            item to write to

        """
        if isinstance(f, str):
            f = open(f,'w')
        f.write("VARIOGRAM {0}\n".format(self.name))
        f.write("  VARTYPE {0}\n".format(self.vartype))
        f.write("  A {0}\n".format(self.a))
        f.write("  ANISOTROPY {0}\n".format(self.anisotropy))
        f.write("  BEARING {0}\n".format(self.bearing))
        f.write("END VARIOGRAM\n\n")
write the Vario2d to a PEST-style structure file

        Parameters
        ----------
        f : (str or file handle)
            item to write to