diff options
Diffstat (limited to '2.3-1/src/fortran/lapack/dgeequ.f')
| -rw-r--r-- | 2.3-1/src/fortran/lapack/dgeequ.f | 225 |
1 files changed, 225 insertions, 0 deletions
diff --git a/2.3-1/src/fortran/lapack/dgeequ.f b/2.3-1/src/fortran/lapack/dgeequ.f new file mode 100644 index 00000000..b703116e --- /dev/null +++ b/2.3-1/src/fortran/lapack/dgeequ.f @@ -0,0 +1,225 @@ + SUBROUTINE DGEEQU( M, N, A, LDA, R, C, ROWCND, COLCND, AMAX, + $ INFO ) +* +* -- LAPACK routine (version 3.1) -- +* Univ. of Tennessee, Univ. of California Berkeley and NAG Ltd.. +* November 2006 +* +* .. Scalar Arguments .. + INTEGER INFO, LDA, M, N + DOUBLE PRECISION AMAX, COLCND, ROWCND +* .. +* .. Array Arguments .. + DOUBLE PRECISION A( LDA, * ), C( * ), R( * ) +* .. +* +* Purpose +* ======= +* +* DGEEQU computes row and column scalings intended to equilibrate an +* M-by-N matrix A and reduce its condition number. R returns the row +* scale factors and C the column scale factors, chosen to try to make +* the largest element in each row and column of the matrix B with +* elements B(i,j)=R(i)*A(i,j)*C(j) have absolute value 1. +* +* R(i) and C(j) are restricted to be between SMLNUM = smallest safe +* number and BIGNUM = largest safe number. Use of these scaling +* factors is not guaranteed to reduce the condition number of A but +* works well in practice. +* +* Arguments +* ========= +* +* M (input) INTEGER +* The number of rows of the matrix A. M >= 0. +* +* N (input) INTEGER +* The number of columns of the matrix A. N >= 0. +* +* A (input) DOUBLE PRECISION array, dimension (LDA,N) +* The M-by-N matrix whose equilibration factors are +* to be computed. +* +* LDA (input) INTEGER +* The leading dimension of the array A. LDA >= max(1,M). +* +* R (output) DOUBLE PRECISION array, dimension (M) +* If INFO = 0 or INFO > M, R contains the row scale factors +* for A. +* +* C (output) DOUBLE PRECISION array, dimension (N) +* If INFO = 0, C contains the column scale factors for A. +* +* ROWCND (output) DOUBLE PRECISION +* If INFO = 0 or INFO > M, ROWCND contains the ratio of the +* smallest R(i) to the largest R(i). If ROWCND >= 0.1 and +* AMAX is neither too large nor too small, it is not worth +* scaling by R. +* +* COLCND (output) DOUBLE PRECISION +* If INFO = 0, COLCND contains the ratio of the smallest +* C(i) to the largest C(i). If COLCND >= 0.1, it is not +* worth scaling by C. +* +* AMAX (output) DOUBLE PRECISION +* Absolute value of largest matrix element. If AMAX is very +* close to overflow or very close to underflow, the matrix +* should be scaled. +* +* INFO (output) INTEGER +* = 0: successful exit +* < 0: if INFO = -i, the i-th argument had an illegal value +* > 0: if INFO = i, and i is +* <= M: the i-th row of A is exactly zero +* > M: the (i-M)-th column of A is exactly zero +* +* ===================================================================== +* +* .. Parameters .. + DOUBLE PRECISION ONE, ZERO + PARAMETER ( ONE = 1.0D+0, ZERO = 0.0D+0 ) +* .. +* .. Local Scalars .. + INTEGER I, J + DOUBLE PRECISION BIGNUM, RCMAX, RCMIN, SMLNUM +* .. +* .. External Functions .. + DOUBLE PRECISION DLAMCH + EXTERNAL DLAMCH +* .. +* .. External Subroutines .. + EXTERNAL XERBLA +* .. +* .. Intrinsic Functions .. + INTRINSIC ABS, MAX, MIN +* .. +* .. Executable Statements .. +* +* Test the input parameters. +* + INFO = 0 + IF( M.LT.0 ) THEN + INFO = -1 + ELSE IF( N.LT.0 ) THEN + INFO = -2 + ELSE IF( LDA.LT.MAX( 1, M ) ) THEN + INFO = -4 + END IF + IF( INFO.NE.0 ) THEN + CALL XERBLA( 'DGEEQU', -INFO ) + RETURN + END IF +* +* Quick return if possible +* + IF( M.EQ.0 .OR. N.EQ.0 ) THEN + ROWCND = ONE + COLCND = ONE + AMAX = ZERO + RETURN + END IF +* +* Get machine constants. +* + SMLNUM = DLAMCH( 'S' ) + BIGNUM = ONE / SMLNUM +* +* Compute row scale factors. +* + DO 10 I = 1, M + R( I ) = ZERO + 10 CONTINUE +* +* Find the maximum element in each row. +* + DO 30 J = 1, N + DO 20 I = 1, M + R( I ) = MAX( R( I ), ABS( A( I, J ) ) ) + 20 CONTINUE + 30 CONTINUE +* +* Find the maximum and minimum scale factors. +* + RCMIN = BIGNUM + RCMAX = ZERO + DO 40 I = 1, M + RCMAX = MAX( RCMAX, R( I ) ) + RCMIN = MIN( RCMIN, R( I ) ) + 40 CONTINUE + AMAX = RCMAX +* + IF( RCMIN.EQ.ZERO ) THEN +* +* Find the first zero scale factor and return an error code. +* + DO 50 I = 1, M + IF( R( I ).EQ.ZERO ) THEN + INFO = I + RETURN + END IF + 50 CONTINUE + ELSE +* +* Invert the scale factors. +* + DO 60 I = 1, M + R( I ) = ONE / MIN( MAX( R( I ), SMLNUM ), BIGNUM ) + 60 CONTINUE +* +* Compute ROWCND = min(R(I)) / max(R(I)) +* + ROWCND = MAX( RCMIN, SMLNUM ) / MIN( RCMAX, BIGNUM ) + END IF +* +* Compute column scale factors +* + DO 70 J = 1, N + C( J ) = ZERO + 70 CONTINUE +* +* Find the maximum element in each column, +* assuming the row scaling computed above. +* + DO 90 J = 1, N + DO 80 I = 1, M + C( J ) = MAX( C( J ), ABS( A( I, J ) )*R( I ) ) + 80 CONTINUE + 90 CONTINUE +* +* Find the maximum and minimum scale factors. +* + RCMIN = BIGNUM + RCMAX = ZERO + DO 100 J = 1, N + RCMIN = MIN( RCMIN, C( J ) ) + RCMAX = MAX( RCMAX, C( J ) ) + 100 CONTINUE +* + IF( RCMIN.EQ.ZERO ) THEN +* +* Find the first zero scale factor and return an error code. +* + DO 110 J = 1, N + IF( C( J ).EQ.ZERO ) THEN + INFO = M + J + RETURN + END IF + 110 CONTINUE + ELSE +* +* Invert the scale factors. +* + DO 120 J = 1, N + C( J ) = ONE / MIN( MAX( C( J ), SMLNUM ), BIGNUM ) + 120 CONTINUE +* +* Compute COLCND = min(C(J)) / max(C(J)) +* + COLCND = MAX( RCMIN, SMLNUM ) / MIN( RCMAX, BIGNUM ) + END IF +* + RETURN +* +* End of DGEEQU +* + END |