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.
