relibc_openlibm/slatec/dwnlt2.f

*DECK DWNLT2
      LOGICAL FUNCTION DWNLT2 (ME, MEND, IR, FACTOR, TAU, SCALE, WIC)
C***BEGIN PROLOGUE  DWNLT2
C***SUBSIDIARY
C***PURPOSE  Subsidiary to WNLIT
C***LIBRARY   SLATEC
C***TYPE      DOUBLE PRECISION (WNLT2-S, DWNLT2-D)
C***AUTHOR  Hanson, R. J., (SNLA)
C           Haskell, K. H., (SNLA)
C***DESCRIPTION
C
C     To test independence of incoming column.
C
C     Test the column IC to determine if it is linearly independent
C     of the columns already in the basis.  In the initial tri. step,
C     we usually want the heavy weight ALAMDA to be included in the
C     test for independence.  In this case, the value of FACTOR will
C     have been set to 1.E0 before this procedure is invoked.
C     In the potentially rank deficient problem, the value of FACTOR
C     will have been set to ALSQ=ALAMDA**2 to remove the effect of the
C     heavy weight from the test for independence.
C
C     Write new column as partitioned vector
C           (A1)  number of components in solution so far = NIV
C           (A2)  M-NIV components
C     And compute  SN = inverse weighted length of A1
C                  RN = inverse weighted length of A2
C     Call the column independent when RN .GT. TAU*SN
C
C***SEE ALSO  DWNLIT
C***ROUTINES CALLED  (NONE)
C***REVISION HISTORY  (YYMMDD)
C   790701  DATE WRITTEN
C   890620  Code extracted from WNLIT and made a subroutine.  (RWC))
C   900604  DP version created from SP version.  (RWC)
C***END PROLOGUE  DWNLT2
      DOUBLE PRECISION FACTOR, SCALE(*), TAU, WIC(*)
      INTEGER IR, ME, MEND
C
      DOUBLE PRECISION RN, SN, T
      INTEGER J
C
C***FIRST EXECUTABLE STATEMENT  DWNLT2
      SN = 0.E0
      RN = 0.E0
      DO 10 J=1,MEND
         T = SCALE(J)
         IF (J.LE.ME) T = T/FACTOR
         T = T*WIC(J)**2
C
         IF (J.LT.IR) THEN
            SN = SN + T
         ELSE
            RN = RN + T
         ENDIF
   10 CONTINUE
      DWNLT2 = RN .GT. SN*TAU**2
      RETURN
      END