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- *DECK DBKSOL
- SUBROUTINE DBKSOL (N, A, X)
- C***BEGIN PROLOGUE DBKSOL
- C***SUBSIDIARY
- C***PURPOSE Subsidiary to DBVSUP
- C***LIBRARY SLATEC
- C***TYPE DOUBLE PRECISION (BKSOL-S, DBKSOL-D)
- C***AUTHOR Watts, H. A., (SNLA)
- C***DESCRIPTION
- C
- C **********************************************************************
- C Solution of an upper triangular linear system by
- C back-substitution
- C
- C The matrix A is assumed to be stored in a linear
- C array proceeding in a row-wise manner. The
- C vector X contains the given constant vector on input
- C and contains the solution on return.
- C The actual diagonal of A is unity while a diagonal
- C scaling matrix is stored there.
- C **********************************************************************
- C
- C***SEE ALSO DBVSUP
- C***ROUTINES CALLED DDOT
- 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 DBKSOL
- C
- DOUBLE PRECISION DDOT
- INTEGER J, K, M, N, NM1
- DOUBLE PRECISION A(*), X(*)
- C
- C***FIRST EXECUTABLE STATEMENT DBKSOL
- M = (N*(N + 1))/2
- X(N) = X(N)*A(M)
- NM1 = N - 1
- IF (NM1 .LT. 1) GO TO 20
- DO 10 K = 1, NM1
- J = N - K
- M = M - K - 1
- X(J) = X(J)*A(M) - DDOT(K,A(M+1),1,X(J+1),1)
- 10 CONTINUE
- 20 CONTINUE
- C
- RETURN
- END
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