splines being polynomials
(use a transform for trigonometric splines to achieve that),
you could have a look at
You can deal with polynomials in several variables (class
PolynomialM) having rational coefficients or
meromorphic functions (quotients of two polynomials, even
in many variables), although the cancellation
of common factors sometimes needs some additional work.
There is a method substitute for evaluating these at different
values for the individual variables.