DINTRV(3)

SYNOPSIS
SUBROUTINE DINTRV (XT, LXT, X, ILO, ILEFT, MFLAG)

NAME
dintrv - Compute the largest integer ILEFT in 1 .LE. ILEFT .LE. LXT such that XT(ILEFT) .LE. X where XT(*) is a subdivision of the X interval.

LIBRARY
SLATEC

CATEGORY
E3, K6

TYPE
DOUBLE PRECISION (INTRV-S, DINTRV-D)

KEYWORDS
B-SPLINE, DATA FITTING, INTERPOLATION, SPLINES

AUTHOR
Amos, D. E., (SNLA)

DESCRIPTION
Written by Carl de Boor and modified by D. E. Amos Abstract **** a double precision routine **** DINTRV is the INTERV routine of the reference. DINTRV computes the largest integer ILEFT in 1 .LE. ILEFT .LE. LXT such that XT(ILEFT) .LE. X where XT(*) is a subdivision of the X interval. Precisely, X .LT. XT(1) 1 -1 if XT(I) .LE. X .LT. XT(I+1) then ILEFT=I , MFLAG=0 XT(LXT) .LE. X LXT 1, That is, when multiplicities are present in the break point to the left of X, the largest index is taken for ILEFT. Description of Arguments Input XT,X are double precision XT - XT is a knot or break point vector of length LXT LXT - length of the XT vector X - argument ILO - an initialization parameter which must be set to 1 the first time the spline array XT is processed by DINTRV. Output ILO - ILO contains information for efficient process- ing after the initial call and ILO must not be changed by the user. Distinct splines require distinct ILO parameters. ILEFT - largest integer satisfying XT(ILEFT) .LE. X MFLAG - signals when X lies out of bounds Error Conditions None

REFERENCES
Carl de Boor, Package for calculating with B-splines, SIAM Journal on Numerical Analysis 14, 3 (June 1977), pp. 441-472.

ROUTINES CALLED
(NONE)

REVISION HISTORY (YYMMDD)
800901 DATE WRITTEN
890831 Modified array declarations. (WRB)
890831 REVISION DATE from Version 3.2
891214 Prologue converted to Version 4.0 format. (BAB)
920501 Reformatted the REFERENCES section. (WRB)