root / src / lapack / double / dlartg.f @ 1
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| 1 | 1 | equemene | SUBROUTINE DLARTG( F, G, CS, SN, R ) |
|---|---|---|---|
| 2 | 1 | equemene | * |
| 3 | 1 | equemene | * -- LAPACK auxiliary routine (version 3.2) -- |
| 4 | 1 | equemene | * -- LAPACK is a software package provided by Univ. of Tennessee, -- |
| 5 | 1 | equemene | * -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..-- |
| 6 | 1 | equemene | * November 2006 |
| 7 | 1 | equemene | * |
| 8 | 1 | equemene | * .. Scalar Arguments .. |
| 9 | 1 | equemene | DOUBLE PRECISION CS, F, G, R, SN |
| 10 | 1 | equemene | * .. |
| 11 | 1 | equemene | * |
| 12 | 1 | equemene | * Purpose |
| 13 | 1 | equemene | * ======= |
| 14 | 1 | equemene | * |
| 15 | 1 | equemene | * DLARTG generate a plane rotation so that |
| 16 | 1 | equemene | * |
| 17 | 1 | equemene | * [ CS SN ] . [ F ] = [ R ] where CS**2 + SN**2 = 1. |
| 18 | 1 | equemene | * [ -SN CS ] [ G ] [ 0 ] |
| 19 | 1 | equemene | * |
| 20 | 1 | equemene | * This is a slower, more accurate version of the BLAS1 routine DROTG, |
| 21 | 1 | equemene | * with the following other differences: |
| 22 | 1 | equemene | * F and G are unchanged on return. |
| 23 | 1 | equemene | * If G=0, then CS=1 and SN=0. |
| 24 | 1 | equemene | * If F=0 and (G .ne. 0), then CS=0 and SN=1 without doing any |
| 25 | 1 | equemene | * floating point operations (saves work in DBDSQR when |
| 26 | 1 | equemene | * there are zeros on the diagonal). |
| 27 | 1 | equemene | * |
| 28 | 1 | equemene | * If F exceeds G in magnitude, CS will be positive. |
| 29 | 1 | equemene | * |
| 30 | 1 | equemene | * Arguments |
| 31 | 1 | equemene | * ========= |
| 32 | 1 | equemene | * |
| 33 | 1 | equemene | * F (input) DOUBLE PRECISION |
| 34 | 1 | equemene | * The first component of vector to be rotated. |
| 35 | 1 | equemene | * |
| 36 | 1 | equemene | * G (input) DOUBLE PRECISION |
| 37 | 1 | equemene | * The second component of vector to be rotated. |
| 38 | 1 | equemene | * |
| 39 | 1 | equemene | * CS (output) DOUBLE PRECISION |
| 40 | 1 | equemene | * The cosine of the rotation. |
| 41 | 1 | equemene | * |
| 42 | 1 | equemene | * SN (output) DOUBLE PRECISION |
| 43 | 1 | equemene | * The sine of the rotation. |
| 44 | 1 | equemene | * |
| 45 | 1 | equemene | * R (output) DOUBLE PRECISION |
| 46 | 1 | equemene | * The nonzero component of the rotated vector. |
| 47 | 1 | equemene | * |
| 48 | 1 | equemene | * This version has a few statements commented out for thread safety |
| 49 | 1 | equemene | * (machine parameters are computed on each entry). 10 feb 03, SJH. |
| 50 | 1 | equemene | * |
| 51 | 1 | equemene | * ===================================================================== |
| 52 | 1 | equemene | * |
| 53 | 1 | equemene | * .. Parameters .. |
| 54 | 1 | equemene | DOUBLE PRECISION ZERO |
| 55 | 1 | equemene | PARAMETER ( ZERO = 0.0D0 ) |
| 56 | 1 | equemene | DOUBLE PRECISION ONE |
| 57 | 1 | equemene | PARAMETER ( ONE = 1.0D0 ) |
| 58 | 1 | equemene | DOUBLE PRECISION TWO |
| 59 | 1 | equemene | PARAMETER ( TWO = 2.0D0 ) |
| 60 | 1 | equemene | * .. |
| 61 | 1 | equemene | * .. Local Scalars .. |
| 62 | 1 | equemene | * LOGICAL FIRST |
| 63 | 1 | equemene | INTEGER COUNT, I |
| 64 | 1 | equemene | DOUBLE PRECISION EPS, F1, G1, SAFMIN, SAFMN2, SAFMX2, SCALE |
| 65 | 1 | equemene | * .. |
| 66 | 1 | equemene | * .. External Functions .. |
| 67 | 1 | equemene | DOUBLE PRECISION DLAMCH |
| 68 | 1 | equemene | EXTERNAL DLAMCH |
| 69 | 1 | equemene | * .. |
| 70 | 1 | equemene | * .. Intrinsic Functions .. |
| 71 | 1 | equemene | INTRINSIC ABS, INT, LOG, MAX, SQRT |
| 72 | 1 | equemene | * .. |
| 73 | 1 | equemene | * .. Save statement .. |
| 74 | 1 | equemene | * SAVE FIRST, SAFMX2, SAFMIN, SAFMN2 |
| 75 | 1 | equemene | * .. |
| 76 | 1 | equemene | * .. Data statements .. |
| 77 | 1 | equemene | * DATA FIRST / .TRUE. / |
| 78 | 1 | equemene | * .. |
| 79 | 1 | equemene | * .. Executable Statements .. |
| 80 | 1 | equemene | * |
| 81 | 1 | equemene | * IF( FIRST ) THEN |
| 82 | 1 | equemene | SAFMIN = DLAMCH( 'S' ) |
| 83 | 1 | equemene | EPS = DLAMCH( 'E' ) |
| 84 | 1 | equemene | SAFMN2 = DLAMCH( 'B' )**INT( LOG( SAFMIN / EPS ) / |
| 85 | 1 | equemene | $ LOG( DLAMCH( 'B' ) ) / TWO ) |
| 86 | 1 | equemene | SAFMX2 = ONE / SAFMN2 |
| 87 | 1 | equemene | * FIRST = .FALSE. |
| 88 | 1 | equemene | * END IF |
| 89 | 1 | equemene | IF( G.EQ.ZERO ) THEN |
| 90 | 1 | equemene | CS = ONE |
| 91 | 1 | equemene | SN = ZERO |
| 92 | 1 | equemene | R = F |
| 93 | 1 | equemene | ELSE IF( F.EQ.ZERO ) THEN |
| 94 | 1 | equemene | CS = ZERO |
| 95 | 1 | equemene | SN = ONE |
| 96 | 1 | equemene | R = G |
| 97 | 1 | equemene | ELSE |
| 98 | 1 | equemene | F1 = F |
| 99 | 1 | equemene | G1 = G |
| 100 | 1 | equemene | SCALE = MAX( ABS( F1 ), ABS( G1 ) ) |
| 101 | 1 | equemene | IF( SCALE.GE.SAFMX2 ) THEN |
| 102 | 1 | equemene | COUNT = 0 |
| 103 | 1 | equemene | 10 CONTINUE |
| 104 | 1 | equemene | COUNT = COUNT + 1 |
| 105 | 1 | equemene | F1 = F1*SAFMN2 |
| 106 | 1 | equemene | G1 = G1*SAFMN2 |
| 107 | 1 | equemene | SCALE = MAX( ABS( F1 ), ABS( G1 ) ) |
| 108 | 1 | equemene | IF( SCALE.GE.SAFMX2 ) |
| 109 | 1 | equemene | $ GO TO 10 |
| 110 | 1 | equemene | R = SQRT( F1**2+G1**2 ) |
| 111 | 1 | equemene | CS = F1 / R |
| 112 | 1 | equemene | SN = G1 / R |
| 113 | 1 | equemene | DO 20 I = 1, COUNT |
| 114 | 1 | equemene | R = R*SAFMX2 |
| 115 | 1 | equemene | 20 CONTINUE |
| 116 | 1 | equemene | ELSE IF( SCALE.LE.SAFMN2 ) THEN |
| 117 | 1 | equemene | COUNT = 0 |
| 118 | 1 | equemene | 30 CONTINUE |
| 119 | 1 | equemene | COUNT = COUNT + 1 |
| 120 | 1 | equemene | F1 = F1*SAFMX2 |
| 121 | 1 | equemene | G1 = G1*SAFMX2 |
| 122 | 1 | equemene | SCALE = MAX( ABS( F1 ), ABS( G1 ) ) |
| 123 | 1 | equemene | IF( SCALE.LE.SAFMN2 ) |
| 124 | 1 | equemene | $ GO TO 30 |
| 125 | 1 | equemene | R = SQRT( F1**2+G1**2 ) |
| 126 | 1 | equemene | CS = F1 / R |
| 127 | 1 | equemene | SN = G1 / R |
| 128 | 1 | equemene | DO 40 I = 1, COUNT |
| 129 | 1 | equemene | R = R*SAFMN2 |
| 130 | 1 | equemene | 40 CONTINUE |
| 131 | 1 | equemene | ELSE |
| 132 | 1 | equemene | R = SQRT( F1**2+G1**2 ) |
| 133 | 1 | equemene | CS = F1 / R |
| 134 | 1 | equemene | SN = G1 / R |
| 135 | 1 | equemene | END IF |
| 136 | 1 | equemene | IF( ABS( F ).GT.ABS( G ) .AND. CS.LT.ZERO ) THEN |
| 137 | 1 | equemene | CS = -CS |
| 138 | 1 | equemene | SN = -SN |
| 139 | 1 | equemene | R = -R |
| 140 | 1 | equemene | END IF |
| 141 | 1 | equemene | END IF |
| 142 | 1 | equemene | RETURN |
| 143 | 1 | equemene | * |
| 144 | 1 | equemene | * End of DLARTG |
| 145 | 1 | equemene | * |
| 146 | 1 | equemene | END |