BS3VL

This function Evaluates a three-dimensional tensor-product spline, given its tensor-product B-spline representation.

Function Return Value

BS3VL — Value of the spline at (X, Y, Z). (Output)

Required Arguments

X — X-coordinate of the point at which the spline is to be evaluated. (Input)

Y — Y-coordinate of the point at which the spline is to be evaluated. (Input)

Z — Z-coordinate of the point at which the spline is to be evaluated. (Input)

KXORD — Order of the spline in the X-direction. (Input)

KYORD — Order of the spline in the Y-direction. (Input)

KZORD — Order of the spline in the Z-direction. (Input)

XKNOT — Array of length NXCOEF + KXORD containing the knot sequence in the X-direction. (Input)
XKNOT must be nondecreasing.

YKNOT — Array of length NYCOEF + KYORD containing the knot sequence in the Y-direction. (Input)
YKNOT must be nondecreasing.

ZKNOT — Array of length NZCOEF + KZORD containing the knot sequence in the Z-direction. (Input)
ZKNOT must be nondecreasing.

NXCOEF — Number of B-spline coefficients in the X-direction. (Input)

NYCOEF — Number of B-spline coefficients in the Y-direction. (Input)

NZCOEF — Number of B-spline coefficients in the Z-direction. (Input)

BSCOEF — Array of length NXCOEF * NYCOEF * NZCOEF containing the tensor-product B-spline coefficients. (Input)
BSCOEF is treated internally as a matrix of size NXCOEF by NYCOEF by NZCOEF.

FORTRAN 90 Interface

Generic: BS3VL (X, Y, Z, KXORD, KYORD, KZORD, XKNOT, YKNOT, ZKNOT, NXCOEF, NYCOEF, NZCOEF, BSCOEF)

Specific: The specific interface names are S_BS3VL and D_BS3VL.

FORTRAN 77 Interface

Single: BS3VL (X, Y, Z, KXORD, KYORD, KZORD, XKNOT, YKNOT, ZKNOT, NXCOEF, NYCOEF, NZCOEF, BSCOEF)

Double: The double precision function name is DBS3VL.

Description

The function BS3VL evaluates a trivariate tensor-product spline (represented as a linear combination of tensor-product B-splines) at a given point. This routine is a special case of the IMSL routine BS3DR, which evaluates a partial derivative of such a spline. (The value of a spline is its zero-th derivative.) For more information, see de Boor (1978, pages 351− 353).

This routine returns the value of the function s at a point (x, y, z) given the coefficients c by computing

 

where kx, ky, and kz are the orders of the splines. (These numbers are passed to the subroutine in KXORD, KYORD, and KZORD, respectively.) Likewise, tx, ty, and tz are the corresponding knot sequences (XKNOT, YKNOT, and ZKNOT).

Comments

Workspace may be explicitly provided, if desired, by use of B23VL/DB23VL. The reference is:

CALL B23VL (X, Y, Z, KXORD, KYORD, KZORD, XKNOT, YKNOT, ZKNOT, NXCOEF, NYCOEF, NZCOEF, BSCOEF, WK)

The additional argument is:

WK — Work array of length 3 * MAX(KXORD, KYORD, KZORD) + KYORD * KZORD + KZORD.

Example

For an example of the use of BS3VL, see IMSL routine BS3IN.