POLYVAL Evaluate polynomial.
    Y = POLYVAL(P,X), when P is a vector of length N+1 whose elements
    are the coefficients of a polynomial, is the value of the
    polynomial evaluated at X.
 
        Y = P(1)*X^N + P(2)*X^(N-1) + ... + P(N)*X + P(N+1)
 
    If X is a matrix or vector, the polynomial is evaluated at all
    points in X.  See also POLYVALM for evaluation in a matrix sense.
 
    Y = POLYVAL(P,X,[],MU) uses XHAT = (X-MU(1))/MU(2) in place of X.
    The centering and scaling parameters MU are optional output
    computed by POLYFIT.
 
    [Y,DELTA] = POLYVAL(P,X,S) or [Y,DELTA] = POLYVAL(P,X,S,MU) uses
    the optional output structure S provided by POLYFIT to generate
    error estimates, Y +/- delta.  If the errors in the data input to
    POLYFIT are independent normal with constant variance, Y +/- DELTA
    contains at least 50% of the predictions.
 
    See also POLYFIT, POLYVALM.