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author | yash1112 | 2017-07-07 21:20:49 +0530 |
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committer | yash1112 | 2017-07-07 21:20:49 +0530 |
commit | 3f52712f806fbd80d66dfdcaff401e5cf94dcca4 (patch) | |
tree | a8333b8187cb44b505b9fe37fc9a7ac8a1711c10 /src/fortran/lapack/zlarfg.f | |
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sci2c arduino updated
Diffstat (limited to 'src/fortran/lapack/zlarfg.f')
-rw-r--r-- | src/fortran/lapack/zlarfg.f | 145 |
1 files changed, 145 insertions, 0 deletions
diff --git a/src/fortran/lapack/zlarfg.f b/src/fortran/lapack/zlarfg.f new file mode 100644 index 0000000..d024f92 --- /dev/null +++ b/src/fortran/lapack/zlarfg.f @@ -0,0 +1,145 @@ + SUBROUTINE ZLARFG( N, ALPHA, X, INCX, TAU ) +* +* -- LAPACK auxiliary routine (version 3.1) -- +* Univ. of Tennessee, Univ. of California Berkeley and NAG Ltd.. +* November 2006 +* +* .. Scalar Arguments .. + INTEGER INCX, N + COMPLEX*16 ALPHA, TAU +* .. +* .. Array Arguments .. + COMPLEX*16 X( * ) +* .. +* +* Purpose +* ======= +* +* ZLARFG generates a complex elementary reflector H of order n, such +* that +* +* H' * ( alpha ) = ( beta ), H' * H = I. +* ( x ) ( 0 ) +* +* where alpha and beta are scalars, with beta real, and x is an +* (n-1)-element complex vector. H is represented in the form +* +* H = I - tau * ( 1 ) * ( 1 v' ) , +* ( v ) +* +* where tau is a complex scalar and v is a complex (n-1)-element +* vector. Note that H is not hermitian. +* +* If the elements of x are all zero and alpha is real, then tau = 0 +* and H is taken to be the unit matrix. +* +* Otherwise 1 <= real(tau) <= 2 and abs(tau-1) <= 1 . +* +* Arguments +* ========= +* +* N (input) INTEGER +* The order of the elementary reflector. +* +* ALPHA (input/output) COMPLEX*16 +* On entry, the value alpha. +* On exit, it is overwritten with the value beta. +* +* X (input/output) COMPLEX*16 array, dimension +* (1+(N-2)*abs(INCX)) +* On entry, the vector x. +* On exit, it is overwritten with the vector v. +* +* INCX (input) INTEGER +* The increment between elements of X. INCX > 0. +* +* TAU (output) COMPLEX*16 +* The value tau. +* +* ===================================================================== +* +* .. Parameters .. + DOUBLE PRECISION ONE, ZERO + PARAMETER ( ONE = 1.0D+0, ZERO = 0.0D+0 ) +* .. +* .. Local Scalars .. + INTEGER J, KNT + DOUBLE PRECISION ALPHI, ALPHR, BETA, RSAFMN, SAFMIN, XNORM +* .. +* .. External Functions .. + DOUBLE PRECISION DLAMCH, DLAPY3, DZNRM2 + COMPLEX*16 ZLADIV + EXTERNAL DLAMCH, DLAPY3, DZNRM2, ZLADIV +* .. +* .. Intrinsic Functions .. + INTRINSIC ABS, DBLE, DCMPLX, DIMAG, SIGN +* .. +* .. External Subroutines .. + EXTERNAL ZDSCAL, ZSCAL +* .. +* .. Executable Statements .. +* + IF( N.LE.0 ) THEN + TAU = ZERO + RETURN + END IF +* + XNORM = DZNRM2( N-1, X, INCX ) + ALPHR = DBLE( ALPHA ) + ALPHI = DIMAG( ALPHA ) +* + IF( XNORM.EQ.ZERO .AND. ALPHI.EQ.ZERO ) THEN +* +* H = I +* + TAU = ZERO + ELSE +* +* general case +* + BETA = -SIGN( DLAPY3( ALPHR, ALPHI, XNORM ), ALPHR ) + SAFMIN = DLAMCH( 'S' ) / DLAMCH( 'E' ) + RSAFMN = ONE / SAFMIN +* + IF( ABS( BETA ).LT.SAFMIN ) THEN +* +* XNORM, BETA may be inaccurate; scale X and recompute them +* + KNT = 0 + 10 CONTINUE + KNT = KNT + 1 + CALL ZDSCAL( N-1, RSAFMN, X, INCX ) + BETA = BETA*RSAFMN + ALPHI = ALPHI*RSAFMN + ALPHR = ALPHR*RSAFMN + IF( ABS( BETA ).LT.SAFMIN ) + $ GO TO 10 +* +* New BETA is at most 1, at least SAFMIN +* + XNORM = DZNRM2( N-1, X, INCX ) + ALPHA = DCMPLX( ALPHR, ALPHI ) + BETA = -SIGN( DLAPY3( ALPHR, ALPHI, XNORM ), ALPHR ) + TAU = DCMPLX( ( BETA-ALPHR ) / BETA, -ALPHI / BETA ) + ALPHA = ZLADIV( DCMPLX( ONE ), ALPHA-BETA ) + CALL ZSCAL( N-1, ALPHA, X, INCX ) +* +* If ALPHA is subnormal, it may lose relative accuracy +* + ALPHA = BETA + DO 20 J = 1, KNT + ALPHA = ALPHA*SAFMIN + 20 CONTINUE + ELSE + TAU = DCMPLX( ( BETA-ALPHR ) / BETA, -ALPHI / BETA ) + ALPHA = ZLADIV( DCMPLX( ONE ), ALPHA-BETA ) + CALL ZSCAL( N-1, ALPHA, X, INCX ) + ALPHA = BETA + END IF + END IF +* + RETURN +* +* End of ZLARFG +* + END |