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- *DECK OHTROL
- SUBROUTINE OHTROL (Q, N, NRDA, DIAG, IRANK, DIV, TD)
- C***BEGIN PROLOGUE OHTROL
- C***SUBSIDIARY
- C***PURPOSE Subsidiary to BVSUP
- C***LIBRARY SLATEC
- C***TYPE SINGLE PRECISION (OHTROL-S, DOHTRL-D)
- C***AUTHOR Watts, H. A., (SNLA)
- C***DESCRIPTION
- C
- C For a rank deficient problem, additional orthogonal
- C HOUSEHOLDER transformations are applied to the left side
- C of Q to further reduce the triangular form.
- C Thus, after application of the routines ORTHOR and OHTROL
- C to the original matrix, the result is a nonsingular
- C triangular matrix while the remainder of the matrix
- C has been zeroed out.
- C
- C***SEE ALSO BVSUP
- C***ROUTINES CALLED SDOT
- C***REVISION HISTORY (YYMMDD)
- C 750601 DATE WRITTEN
- C 890831 Modified array declarations. (WRB)
- C 891214 Prologue converted to Version 4.0 format. (BAB)
- C 900328 Added TYPE section. (WRB)
- C 910722 Updated AUTHOR section. (ALS)
- C***END PROLOGUE OHTROL
- DIMENSION Q(NRDA,*),DIAG(*),DIV(*),TD(*)
- C***FIRST EXECUTABLE STATEMENT OHTROL
- NMIR=N-IRANK
- IRP=IRANK+1
- DO 30 K=1,IRANK
- KIR=IRP-K
- DIAGK=DIAG(KIR)
- SIG=(DIAGK*DIAGK)+SDOT(NMIR,Q(IRP,KIR),1,Q(IRP,KIR),1)
- DD=SIGN(SQRT(SIG),-DIAGK)
- DIV(KIR)=DD
- TDV=DIAGK-DD
- TD(KIR)=TDV
- IF (K .EQ. IRANK) GO TO 30
- KIRM=KIR-1
- SQD=DD*DIAGK-SIG
- DO 20 J=1,KIRM
- QS=((TDV*Q(KIR,J))+SDOT(NMIR,Q(IRP,J),1,Q(IRP,KIR),1))
- 1 /SQD
- Q(KIR,J)=Q(KIR,J)+QS*TDV
- DO 10 L=IRP,N
- 10 Q(L,J)=Q(L,J)+QS*Q(L,KIR)
- 20 CONTINUE
- 30 CONTINUE
- RETURN
- END
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