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Diffstat (limited to 'src/fortran/lapack/dlartg.f')
| -rw-r--r-- | src/fortran/lapack/dlartg.f | 145 |
1 files changed, 145 insertions, 0 deletions
diff --git a/src/fortran/lapack/dlartg.f b/src/fortran/lapack/dlartg.f new file mode 100644 index 0000000..eb807c1 --- /dev/null +++ b/src/fortran/lapack/dlartg.f @@ -0,0 +1,145 @@ + SUBROUTINE DLARTG( F, G, CS, SN, R ) +* +* -- LAPACK auxiliary routine (version 3.1) -- +* Univ. of Tennessee, Univ. of California Berkeley and NAG Ltd.. +* November 2006 +* +* .. Scalar Arguments .. + DOUBLE PRECISION CS, F, G, R, SN +* .. +* +* Purpose +* ======= +* +* DLARTG generate a plane rotation so that +* +* [ CS SN ] . [ F ] = [ R ] where CS**2 + SN**2 = 1. +* [ -SN CS ] [ G ] [ 0 ] +* +* This is a slower, more accurate version of the BLAS1 routine DROTG, +* with the following other differences: +* F and G are unchanged on return. +* If G=0, then CS=1 and SN=0. +* If F=0 and (G .ne. 0), then CS=0 and SN=1 without doing any +* floating point operations (saves work in DBDSQR when +* there are zeros on the diagonal). +* +* If F exceeds G in magnitude, CS will be positive. +* +* Arguments +* ========= +* +* F (input) DOUBLE PRECISION +* The first component of vector to be rotated. +* +* G (input) DOUBLE PRECISION +* The second component of vector to be rotated. +* +* CS (output) DOUBLE PRECISION +* The cosine of the rotation. +* +* SN (output) DOUBLE PRECISION +* The sine of the rotation. +* +* R (output) DOUBLE PRECISION +* The nonzero component of the rotated vector. +* +* This version has a few statements commented out for thread safety +* (machine parameters are computed on each entry). 10 feb 03, SJH. +* +* ===================================================================== +* +* .. Parameters .. + DOUBLE PRECISION ZERO + PARAMETER ( ZERO = 0.0D0 ) + DOUBLE PRECISION ONE + PARAMETER ( ONE = 1.0D0 ) + DOUBLE PRECISION TWO + PARAMETER ( TWO = 2.0D0 ) +* .. +* .. Local Scalars .. +* LOGICAL FIRST + INTEGER COUNT, I + DOUBLE PRECISION EPS, F1, G1, SAFMIN, SAFMN2, SAFMX2, SCALE +* .. +* .. External Functions .. + DOUBLE PRECISION DLAMCH + EXTERNAL DLAMCH +* .. +* .. Intrinsic Functions .. + INTRINSIC ABS, INT, LOG, MAX, SQRT +* .. +* .. Save statement .. +* SAVE FIRST, SAFMX2, SAFMIN, SAFMN2 +* .. +* .. Data statements .. +* DATA FIRST / .TRUE. / +* .. +* .. Executable Statements .. +* +* IF( FIRST ) THEN + SAFMIN = DLAMCH( 'S' ) + EPS = DLAMCH( 'E' ) + SAFMN2 = DLAMCH( 'B' )**INT( LOG( SAFMIN / EPS ) / + $ LOG( DLAMCH( 'B' ) ) / TWO ) + SAFMX2 = ONE / SAFMN2 +* FIRST = .FALSE. +* END IF + IF( G.EQ.ZERO ) THEN + CS = ONE + SN = ZERO + R = F + ELSE IF( F.EQ.ZERO ) THEN + CS = ZERO + SN = ONE + R = G + ELSE + F1 = F + G1 = G + SCALE = MAX( ABS( F1 ), ABS( G1 ) ) + IF( SCALE.GE.SAFMX2 ) THEN + COUNT = 0 + 10 CONTINUE + COUNT = COUNT + 1 + F1 = F1*SAFMN2 + G1 = G1*SAFMN2 + SCALE = MAX( ABS( F1 ), ABS( G1 ) ) + IF( SCALE.GE.SAFMX2 ) + $ GO TO 10 + R = SQRT( F1**2+G1**2 ) + CS = F1 / R + SN = G1 / R + DO 20 I = 1, COUNT + R = R*SAFMX2 + 20 CONTINUE + ELSE IF( SCALE.LE.SAFMN2 ) THEN + COUNT = 0 + 30 CONTINUE + COUNT = COUNT + 1 + F1 = F1*SAFMX2 + G1 = G1*SAFMX2 + SCALE = MAX( ABS( F1 ), ABS( G1 ) ) + IF( SCALE.LE.SAFMN2 ) + $ GO TO 30 + R = SQRT( F1**2+G1**2 ) + CS = F1 / R + SN = G1 / R + DO 40 I = 1, COUNT + R = R*SAFMN2 + 40 CONTINUE + ELSE + R = SQRT( F1**2+G1**2 ) + CS = F1 / R + SN = G1 / R + END IF + IF( ABS( F ).GT.ABS( G ) .AND. CS.LT.ZERO ) THEN + CS = -CS + SN = -SN + R = -R + END IF + END IF + RETURN +* +* End of DLARTG +* + END |