ppval

Evaluate piecewise polynomial

Syntax

v = ppval(pp,xx)

Description

v = ppval(pp,xx) returns the value of the piecewise polynomial f, contained in pp, at the entries of xx. You can construct pp using the functions pchip, spline, or the spline utility mkpp.

v is obtained by replacing each entry of xx by the value of f there. If f is scalar-valued, v is of the same size as xx. xx may be N-dimensional.

If pp was constructed by pchip, spline, or mkpp using the orientation of non-scalar function values specified for those functions, then:

If f is [D1,..,Dr]-valued, and xx is a vector of length N, then V has size [D1,...,Dr, N], with V(:,...,:,J) the value of f at xx(J).

If f is [D1,..,Dr]-valued, and xx has size [N1,...,Ns], then V has size [D1,...,Dr, N1,...,Ns], with V(:,...,:, J1,...,Js) the value of f at xx(J1,...,Js).

Examples

Compare the result of integrating cos(x) between 0 and 10 to the result of integrating a piece-wise polynomial approximation of the same function.

a = 0; b = 10;
int1 = integral(@cos,a,b)

int1 =
   -0.5440

Create a piece-wise polynomial approximation of cos(x) and integrate over the same interval.

x = a:b; 
y = cos(x);
pp = spline(x,y);
int2 = integral(@(x)ppval(pp,x),a,b)

int2 =
   -0.5485

See Also

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