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Diffstat (limited to 'SRC/cgttrs.f')
| -rw-r--r-- | SRC/cgttrs.f | 142 |
1 files changed, 142 insertions, 0 deletions
diff --git a/SRC/cgttrs.f b/SRC/cgttrs.f new file mode 100644 index 00000000..2da12aca --- /dev/null +++ b/SRC/cgttrs.f @@ -0,0 +1,142 @@ + SUBROUTINE CGTTRS( TRANS, N, NRHS, DL, D, DU, DU2, IPIV, B, LDB, + $ INFO ) +* +* -- LAPACK routine (version 3.1) -- +* Univ. of Tennessee, Univ. of California Berkeley and NAG Ltd.. +* November 2006 +* +* .. Scalar Arguments .. + CHARACTER TRANS + INTEGER INFO, LDB, N, NRHS +* .. +* .. Array Arguments .. + INTEGER IPIV( * ) + COMPLEX B( LDB, * ), D( * ), DL( * ), DU( * ), DU2( * ) +* .. +* +* Purpose +* ======= +* +* CGTTRS solves one of the systems of equations +* A * X = B, A**T * X = B, or A**H * X = B, +* with a tridiagonal matrix A using the LU factorization computed +* by CGTTRF. +* +* Arguments +* ========= +* +* TRANS (input) CHARACTER*1 +* Specifies the form of the system of equations. +* = 'N': A * X = B (No transpose) +* = 'T': A**T * X = B (Transpose) +* = 'C': A**H * X = B (Conjugate transpose) +* +* N (input) INTEGER +* The order of the matrix A. +* +* NRHS (input) INTEGER +* The number of right hand sides, i.e., the number of columns +* of the matrix B. NRHS >= 0. +* +* DL (input) COMPLEX array, dimension (N-1) +* The (n-1) multipliers that define the matrix L from the +* LU factorization of A. +* +* D (input) COMPLEX array, dimension (N) +* The n diagonal elements of the upper triangular matrix U from +* the LU factorization of A. +* +* DU (input) COMPLEX array, dimension (N-1) +* The (n-1) elements of the first super-diagonal of U. +* +* DU2 (input) COMPLEX array, dimension (N-2) +* The (n-2) elements of the second super-diagonal of U. +* +* IPIV (input) INTEGER array, dimension (N) +* The pivot indices; for 1 <= i <= n, row i of the matrix was +* interchanged with row IPIV(i). IPIV(i) will always be either +* i or i+1; IPIV(i) = i indicates a row interchange was not +* required. +* +* B (input/output) COMPLEX array, dimension (LDB,NRHS) +* On entry, the matrix of right hand side vectors B. +* On exit, B is overwritten by the solution vectors X. +* +* LDB (input) INTEGER +* The leading dimension of the array B. LDB >= max(1,N). +* +* INFO (output) INTEGER +* = 0: successful exit +* < 0: if INFO = -k, the k-th argument had an illegal value +* +* ===================================================================== +* +* .. Local Scalars .. + LOGICAL NOTRAN + INTEGER ITRANS, J, JB, NB +* .. +* .. External Functions .. + INTEGER ILAENV + EXTERNAL ILAENV +* .. +* .. External Subroutines .. + EXTERNAL CGTTS2, XERBLA +* .. +* .. Intrinsic Functions .. + INTRINSIC MAX, MIN +* .. +* .. Executable Statements .. +* + INFO = 0 + NOTRAN = ( TRANS.EQ.'N' .OR. TRANS.EQ.'n' ) + IF( .NOT.NOTRAN .AND. .NOT.( TRANS.EQ.'T' .OR. TRANS.EQ. + $ 't' ) .AND. .NOT.( TRANS.EQ.'C' .OR. TRANS.EQ.'c' ) ) THEN + INFO = -1 + ELSE IF( N.LT.0 ) THEN + INFO = -2 + ELSE IF( NRHS.LT.0 ) THEN + INFO = -3 + ELSE IF( LDB.LT.MAX( N, 1 ) ) THEN + INFO = -10 + END IF + IF( INFO.NE.0 ) THEN + CALL XERBLA( 'CGTTRS', -INFO ) + RETURN + END IF +* +* Quick return if possible +* + IF( N.EQ.0 .OR. NRHS.EQ.0 ) + $ RETURN +* +* Decode TRANS +* + IF( NOTRAN ) THEN + ITRANS = 0 + ELSE IF( TRANS.EQ.'T' .OR. TRANS.EQ.'t' ) THEN + ITRANS = 1 + ELSE + ITRANS = 2 + END IF +* +* Determine the number of right-hand sides to solve at a time. +* + IF( NRHS.EQ.1 ) THEN + NB = 1 + ELSE + NB = MAX( 1, ILAENV( 1, 'CGTTRS', TRANS, N, NRHS, -1, -1 ) ) + END IF +* + IF( NB.GE.NRHS ) THEN + CALL CGTTS2( ITRANS, N, NRHS, DL, D, DU, DU2, IPIV, B, LDB ) + ELSE + DO 10 J = 1, NRHS, NB + JB = MIN( NRHS-J+1, NB ) + CALL CGTTS2( ITRANS, N, JB, DL, D, DU, DU2, IPIV, B( 1, J ), + $ LDB ) + 10 CONTINUE + END IF +* +* End of CGTTRS +* + END |