func (v *Vec) Set(s string) error {
	if _, err := fmt.Sscanf(s, "(%f,%f)", &v.X, &v.Y); err != nil {
		return fmt.Errorf("invalid syntax \"%s\"", s)
	}
	return nil
}
func (v *Vec) Set(s string) error {
	if _, err := fmt.Sscanf(s, "(%f,%f)", &v.X, &v.Y); err != nil {
		return fmt.Errorf("invalid syntax \"%s\"", s)
	}
	return nil
}
// Set sets the components of the vector from a string of the form
// "float,float"