*DECK PCHCI SUBROUTINE PCHCI (N, H, SLOPE, D, INCFD) C***BEGIN PROLOGUE PCHCI C***SUBSIDIARY C***PURPOSE Set interior derivatives for PCHIC C***LIBRARY SLATEC (PCHIP) C***TYPE SINGLE PRECISION (PCHCI-S, DPCHCI-D) C***AUTHOR Fritsch, F. N., (LLNL) C***DESCRIPTION C C PCHCI: PCHIC Initial Derivative Setter. C C Called by PCHIC to set derivatives needed to determine a monotone C piecewise cubic Hermite interpolant to the data. C C Default boundary conditions are provided which are compatible C with monotonicity. If the data are only piecewise monotonic, the C interpolant will have an extremum at each point where monotonicity C switches direction. C C To facilitate two-dimensional applications, includes an increment C between successive values of the D-array. C C The resulting piecewise cubic Hermite function should be identical C (within roundoff error) to that produced by PCHIM. C C ---------------------------------------------------------------------- C C Calling sequence: C C PARAMETER (INCFD = ...) C INTEGER N C REAL H(N), SLOPE(N), D(INCFD,N) C C CALL PCHCI (N, H, SLOPE, D, INCFD) C C Parameters: C C N -- (input) number of data points. C If N=2, simply does linear interpolation. C C H -- (input) real array of interval lengths. C SLOPE -- (input) real array of data slopes. C If the data are (X(I),Y(I)), I=1(1)N, then these inputs are: C H(I) = X(I+1)-X(I), C SLOPE(I) = (Y(I+1)-Y(I))/H(I), I=1(1)N-1. C C D -- (output) real array of derivative values at the data points. C If the data are monotonic, these values will determine a C a monotone cubic Hermite function. C The value corresponding to X(I) is stored in C D(1+(I-1)*INCFD), I=1(1)N. C No other entries in D are changed. C C INCFD -- (input) increment between successive values in D. C This argument is provided primarily for 2-D applications. C C ------- C WARNING: This routine does no validity-checking of arguments. C ------- C C Fortran intrinsics used: ABS, MAX, MIN. C C***SEE ALSO PCHIC C***ROUTINES CALLED PCHST C***REVISION HISTORY (YYMMDD) C 820218 DATE WRITTEN C 820601 Modified end conditions to be continuous functions of C data when monotonicity switches in next interval. C 820602 1. Modified formulas so end conditions are less prone C to over/underflow problems. C 2. Minor modification to HSUM calculation. C 820805 Converted to SLATEC library version. C 890411 Added SAVE statements (Vers. 3.2). C 890531 Changed all specific intrinsics to generic. (WRB) C 890831 Modified array declarations. (WRB) C 890831 REVISION DATE from Version 3.2 C 891214 Prologue converted to Version 4.0 format. (BAB) C 900328 Added TYPE section. (WRB) C 910408 Updated AUTHOR section in prologue. (WRB) C 930503 Improved purpose. (FNF) C***END PROLOGUE PCHCI