Function: polinterpolate
Section: polynomials
C-Name: polint
Prototype: GDGDGD&
Help: polinterpolate(xa,{ya},{x},{&e}): polynomial interpolation at x
 according to data vectors xa, ya (ie return P such that P(xa[i]) = ya[i] for
 all i). If ya is omitter, return P such that P(i) = xa[i]. If present, e
 will contain an error estimate on the returned value

