FITSPL

Use

The function can be called by any user-defined subroutine.

Format

Fortran Calling Syntax

CALL FITSPL (XVAL, ZVAL, ID, IORD, ARRAY, ERRFLG)

C/C++ Calling Syntax

c_fitspl (xval, zval, id, iord, array, errflg)

Python Calling Syntax

[array, errflg] = py_fitspl (xval, zval, id, iord)

Compose/MATLAB Calling Syntax

[array, errflg] = m_fitspl (xval, zval, id, iord)

Description

FITSPL is a b-spline-based interpolation (3rd order) that requires a minimum of four points on a curve. The spline is a piecewise polynomial function of the 2nd degree. Just as CUBSPL, it is suitable as an input function for motion.

Attributes

XVAL

[double]

The first independent variable of a curve or surface at which the spline function is supposed to interpolate the output value.

ZVAL

[double]

The second independent variable of a surface at which the spline function is supposed to interpolate the output value. Set this value to 0 if only a curve interpolation is needed.

ID

[integer]

The ID of the Reference_Spline element.

IORD

The order of the derivative to be returned by the spline function. Only 0, 1, or 2 are valid entities.

Output

ARRAY

[double]

The vector output value of dimension 3.

• If IORD is 0, then ARRAY(1) contains the computed interpolated value y.
• If IORD is 1, then ARRAY(1) and ARRAY(2) contain the derivatives of y with respect to x and z.
• If IORD is 2, then ARRAY(1), ARRAY(2), and ARRAY(3) contain the second derivatives of y with respect to xx, xz, and zz, respectively.

ERRFLG

[logical]

Logical variable that is returned to the calling subroutine and that indicates the success of the spline function call.

Example

def REQSUB(id, time, par, npar, iflag):
  results = [0.0]*8
  results[0]  = FITSPL(time,0,100,0)
  results[1]  = FITSPL(time,0,100,1)
  results[2]  = FITSPL(time,0,100,2)
  return results