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Diffstat (limited to 'SRC/sgetri.f')
| -rw-r--r-- | SRC/sgetri.f | 192 |
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diff --git a/SRC/sgetri.f b/SRC/sgetri.f new file mode 100644 index 00000000..3eb1f346 --- /dev/null +++ b/SRC/sgetri.f @@ -0,0 +1,192 @@ + SUBROUTINE SGETRI( N, A, LDA, IPIV, WORK, LWORK, INFO ) +* +* -- LAPACK routine (version 3.1) -- +* Univ. of Tennessee, Univ. of California Berkeley and NAG Ltd.. +* November 2006 +* +* .. Scalar Arguments .. + INTEGER INFO, LDA, LWORK, N +* .. +* .. Array Arguments .. + INTEGER IPIV( * ) + REAL A( LDA, * ), WORK( * ) +* .. +* +* Purpose +* ======= +* +* SGETRI computes the inverse of a matrix using the LU factorization +* computed by SGETRF. +* +* This method inverts U and then computes inv(A) by solving the system +* inv(A)*L = inv(U) for inv(A). +* +* Arguments +* ========= +* +* N (input) INTEGER +* The order of the matrix A. N >= 0. +* +* A (input/output) REAL array, dimension (LDA,N) +* On entry, the factors L and U from the factorization +* A = P*L*U as computed by SGETRF. +* On exit, if INFO = 0, the inverse of the original matrix A. +* +* LDA (input) INTEGER +* The leading dimension of the array A. LDA >= max(1,N). +* +* IPIV (input) INTEGER array, dimension (N) +* The pivot indices from SGETRF; for 1<=i<=N, row i of the +* matrix was interchanged with row IPIV(i). +* +* WORK (workspace/output) REAL array, dimension (MAX(1,LWORK)) +* On exit, if INFO=0, then WORK(1) returns the optimal LWORK. +* +* LWORK (input) INTEGER +* The dimension of the array WORK. LWORK >= max(1,N). +* For optimal performance LWORK >= N*NB, where NB is +* the optimal blocksize returned by ILAENV. +* +* If LWORK = -1, then a workspace query is assumed; the routine +* only calculates the optimal size of the WORK array, returns +* this value as the first entry of the WORK array, and no error +* message related to LWORK is issued by XERBLA. +* +* INFO (output) INTEGER +* = 0: successful exit +* < 0: if INFO = -i, the i-th argument had an illegal value +* > 0: if INFO = i, U(i,i) is exactly zero; the matrix is +* singular and its inverse could not be computed. +* +* ===================================================================== +* +* .. Parameters .. + REAL ZERO, ONE + PARAMETER ( ZERO = 0.0E+0, ONE = 1.0E+0 ) +* .. +* .. Local Scalars .. + LOGICAL LQUERY + INTEGER I, IWS, J, JB, JJ, JP, LDWORK, LWKOPT, NB, + $ NBMIN, NN +* .. +* .. External Functions .. + INTEGER ILAENV + EXTERNAL ILAENV +* .. +* .. External Subroutines .. + EXTERNAL SGEMM, SGEMV, SSWAP, STRSM, STRTRI, XERBLA +* .. +* .. Intrinsic Functions .. + INTRINSIC MAX, MIN +* .. +* .. Executable Statements .. +* +* Test the input parameters. +* + INFO = 0 + NB = ILAENV( 1, 'SGETRI', ' ', N, -1, -1, -1 ) + LWKOPT = N*NB + WORK( 1 ) = LWKOPT + LQUERY = ( LWORK.EQ.-1 ) + IF( N.LT.0 ) THEN + INFO = -1 + ELSE IF( LDA.LT.MAX( 1, N ) ) THEN + INFO = -3 + ELSE IF( LWORK.LT.MAX( 1, N ) .AND. .NOT.LQUERY ) THEN + INFO = -6 + END IF + IF( INFO.NE.0 ) THEN + CALL XERBLA( 'SGETRI', -INFO ) + RETURN + ELSE IF( LQUERY ) THEN + RETURN + END IF +* +* Quick return if possible +* + IF( N.EQ.0 ) + $ RETURN +* +* Form inv(U). If INFO > 0 from STRTRI, then U is singular, +* and the inverse is not computed. +* + CALL STRTRI( 'Upper', 'Non-unit', N, A, LDA, INFO ) + IF( INFO.GT.0 ) + $ RETURN +* + NBMIN = 2 + LDWORK = N + IF( NB.GT.1 .AND. NB.LT.N ) THEN + IWS = MAX( LDWORK*NB, 1 ) + IF( LWORK.LT.IWS ) THEN + NB = LWORK / LDWORK + NBMIN = MAX( 2, ILAENV( 2, 'SGETRI', ' ', N, -1, -1, -1 ) ) + END IF + ELSE + IWS = N + END IF +* +* Solve the equation inv(A)*L = inv(U) for inv(A). +* + IF( NB.LT.NBMIN .OR. NB.GE.N ) THEN +* +* Use unblocked code. +* + DO 20 J = N, 1, -1 +* +* Copy current column of L to WORK and replace with zeros. +* + DO 10 I = J + 1, N + WORK( I ) = A( I, J ) + A( I, J ) = ZERO + 10 CONTINUE +* +* Compute current column of inv(A). +* + IF( J.LT.N ) + $ CALL SGEMV( 'No transpose', N, N-J, -ONE, A( 1, J+1 ), + $ LDA, WORK( J+1 ), 1, ONE, A( 1, J ), 1 ) + 20 CONTINUE + ELSE +* +* Use blocked code. +* + NN = ( ( N-1 ) / NB )*NB + 1 + DO 50 J = NN, 1, -NB + JB = MIN( NB, N-J+1 ) +* +* Copy current block column of L to WORK and replace with +* zeros. +* + DO 40 JJ = J, J + JB - 1 + DO 30 I = JJ + 1, N + WORK( I+( JJ-J )*LDWORK ) = A( I, JJ ) + A( I, JJ ) = ZERO + 30 CONTINUE + 40 CONTINUE +* +* Compute current block column of inv(A). +* + IF( J+JB.LE.N ) + $ CALL SGEMM( 'No transpose', 'No transpose', N, JB, + $ N-J-JB+1, -ONE, A( 1, J+JB ), LDA, + $ WORK( J+JB ), LDWORK, ONE, A( 1, J ), LDA ) + CALL STRSM( 'Right', 'Lower', 'No transpose', 'Unit', N, JB, + $ ONE, WORK( J ), LDWORK, A( 1, J ), LDA ) + 50 CONTINUE + END IF +* +* Apply column interchanges. +* + DO 60 J = N - 1, 1, -1 + JP = IPIV( J ) + IF( JP.NE.J ) + $ CALL SSWAP( N, A( 1, J ), 1, A( 1, JP ), 1 ) + 60 CONTINUE +* + WORK( 1 ) = IWS + RETURN +* +* End of SGETRI +* + END |