DPCHCI(3)

SYNOPSIS
SUBROUTINE DPCHCI (N, H, SLOPE, D, INCFD)

NAME
dpchci - Set interior derivatives for DPCHIC

LIBRARY
SLATEC (PCHIP)

TYPE
DOUBLE PRECISION (PCHCI-S, DPCHCI-D)

AUTHOR
Fritsch, F. N., (LLNL)

DESCRIPTION
DPCHCI: DPCHIC Initial Derivative Setter. Called by DPCHIC to set derivatives needed to determine a monotone piecewise cubic Hermite interpolant to the data. Default boundary conditions are provided which are compatible with monotonicity. If the data are only piecewise monotonic, the interpolant will have an extremum at each point where monotonicity switches direction. To facilitate two-dimensional applications, includes an increment between successive values of the D-array. The resulting piecewise cubic Hermite function should be identical (within roundoff error) to that produced by DPCHIM. ---------------------------------------------------------------------- Calling sequence: PARAMETER (INCFD = ...) INTEGER N DOUBLE PRECISION H(N), SLOPE(N), D(INCFD,N) CALL DPCHCI (N, H, SLOPE, D, INCFD) Parameters: N -- (input) number of data points. If N=2, simply does linear interpolation. H -- (input) real*8 array of interval lengths. SLOPE -- (input) real*8 array of data slopes. If the data are (X(I),Y(I)), I=1(1)N, then these inputs are: H(I) = X(I+1)-X(I), SLOPE(I) = (Y(I+1)-Y(I))/H(I), I=1(1)N-1. D -- (output) real*8 array of derivative values at data points. If the data are monotonic, these values will determine a a monotone cubic Hermite function. The value corresponding to X(I) is stored in D(1+(I-1)*INCFD), I=1(1)N. No other entries in D are changed. INCFD -- (input) increment between successive values in D. This argument is provided primarily for 2-D applications. ------- WARNING: This routine does no validity-checking of arguments. ------- Fortran intrinsics used: ABS, MAX, MIN.

SEE ALSO
DPCHIC

ROUTINES CALLED
DPCHST

REVISION HISTORY (YYMMDD)
820218 DATE WRITTEN
820601 Modified end conditions to be continuous functions of data when monotonicity switches in next interval.
820602 1. Modified formulas so end conditions are less prone to over/underflow problems. 2. Minor modification to HSUM calculation.
820805 Converted to SLATEC library version.
870813 Minor cosmetic changes.
890411 Added SAVE statements (Vers. 3.2).
890531 Changed all specific intrinsics to generic. (WRB)
890831 Modified array declarations. (WRB)
890831 REVISION DATE from Version 3.2
891214 Prologue converted to Version 4.0 format. (BAB)
900328 Added TYPE section. (WRB)
910408 Updated AUTHOR section in prologue. (WRB)
930503 Improved purpose. (FNF)