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