/*
 *  call-seq:
 *     Dvector.pm_cubic_interpolate(x, interpolant)  ->  y
 *
 *  Returns the _y_ corresponding to _x_ by pm_cubic interpolation using the _interpolant_
 *  which was previously created by calling _create_pm_cubic_interpolant_.
 *  
 */ 
VALUE dvector_pm_cubic_interpolate(int argc, VALUE *argv, VALUE klass) {