Function: polinterpolate
Section: polynomials
C-Name: polint
Prototype: GDGDGD&
Help: polinterpolate(X,{Y},{x},{&e}): polynomial interpolation at x
 according to data vectors X, Y (ie return P such that P(X[i]) = Y[i] for
 all i). If Y is omitted, return P such that P(i) = X[i]. If present, e
 will contain an error estimate on the returned value.
Doc: given the data vectors
 $X$ and $Y$ of the same length $n$ ($X$ containing the $x$-coordinates,
 and $Y$ the corresponding $y$-coordinates), this function finds the
 \idx{interpolating polynomial} passing through these points and evaluates it
 at~$x$. If $Y$ is omitted, return the polynomial interpolating the
 $(i,X[i])$. If present, $e$ will contain an error estimate on the returned
 value.