CSVAL

This function evaluates a cubic spline.

Function Return Value

CSVAL — Value of the polynomial at X. (Output)

Required Arguments

X — Point at which the spline is to be evaluated. (Input)

BREAK — Array of length NINTV + 1 containing the breakpoints for the piecewise cubic representation. (Input)
BREAK must be strictly increasing.

CSCOEF — Matrix of size 4 by NINTV + 1 containing the local coefficients of the cubic pieces. (Input)

Optional Arguments

NINTV — Number of polynomial pieces. (Input)

FORTRAN 90 Interface

Generic: CSVAL (X, BREAK, CSCOEF[, …])

Specific: The specific interface names are S_CSVAL and D_CSVAL.

FORTRAN 77 Interface

Single: CSVAL (X, NINTV, BREAK, CSCOEF)

Double: The double precision function name is DCSVAL.

Description

The routine CSVAL evaluates a cubic spline at a given point. It is a special case of the routine PPDER, which evaluates the derivative of a piecewise polynomial. (The value of a piecewise polynomial is its zero-th derivative and a cubic spline is a piecewise polynomial of order 4.) The routine PPDER is based on the routine PPVALU in de Boor (1978, page 89).

Example

For an example of the use of CSVAL, see IMSL routine CSINT.