ncl_curvps man page
CURVPS — calculate values for a smoothing spline for a periodic function. To use CURVPS, load the NCAR Graphics library ngmath. curvp2, fitgrid_params. Copyright (C) 2000 The use of this Software is governed by a License Agreement.
CALL CURVPS (N, X, Y, P, D, ISW, S, EPS, YS, YSP, SIGMA, TEMP, IER)
This subroutine calculates certain values that are used by CURVP2 in order to compute an interpolatory smoothing spline under tension through a sequence of functional values for a periodic function. The actual computation of the interpolated values must be done using CURVP2.
Three parameters are used to control the degree of smoothness -- D, S, and EPS.
The parameter D is a value indicating the degree of confidence in the accuracy of the input function values -- it should be an approximation of the standard deviation of error. Effectively the value of D controls how close the smoothed curve comes to the input data points. If D is small then the interpolated curve will pass close to the input data. The larger the value of D, the more freedom the smooth curve has in how close it comes to the input data values.
S is a more subtle global smoothing parameter. S must be non-negative. For small values of S, the curve approximates the tension spline and for larger values of S, the curve is smoother. A reasonable value for S is REAL(N).
EPS controls the precision to which S is interpreted; EPS must be between 0. and 1. inclusive. A reasonable value for EPS is SQRT(2./REAL(N)).
= 1 if N is less than 2.
= 2 if S is negative.
= 3 if EPS is negative or greater than 1.
= 4 if X values are not strictly increasing.
= 5 if D is negative.
= 6 if P is less than or equal to X(N)-X(1).
Complete documentation for Fitgrid is available at URL
University Corporation for Atmospheric Research
To use CURVPS, load the NCAR Graphics library ngmath.
Copyright (C) 2000
The use of this Software is governed by a License Agreement.