The
SPLINE function performs cubic
spline
interpolation.
This routine is written in the IDL language. Its source code can be found in the file
spline.pro
in the
lib
subdirectory of the IDL distribution.
Calling Sequence
Result = SPLINE(
X, Y, T [, Sigma]
)
Arguments
X
The abscissa vector. Values
must
be monotonically increasing.
Y
The vector of ordinate values corresponding to
X
.
T
The vector of abscissa values for which the ordinate is desired. The values of
T must
be monotonically increasing.
Sigma
The amount of "tension" that is applied to the curve. The default value is 1.0. If sigma is close to 0, (e.g., .01), then effectively there is a cubic spline fit. If sigma is large, (e.g., greater than 10), then the fit will be like a polynomial interpolation.
Example
The commands below show a typical use of SPLINE:
X = [2.,3.,4.] ;
X values of original function
Y = (X-3)^2 ;
Make a quadratic
T = FINDGEN(20)/10.+2 ;
Values for interpolated points
