1: SUBROUTINE DROTMG(DD1,DD2,DX1,DY1,DPARAM)
2: * .. Scalar Arguments ..
3: DOUBLE PRECISION DD1,DD2,DX1,DY1
4: * ..
5: * .. Array Arguments ..
6: DOUBLE PRECISION DPARAM(5)
7: * ..
8: *
9: * Purpose
10: * =======
11: *
12: * CONSTRUCT THE MODIFIED GIVENS TRANSFORMATION MATRIX H WHICH ZEROS
13: * THE SECOND COMPONENT OF THE 2-VECTOR (DSQRT(DD1)*DX1,DSQRT(DD2)*
14: * DY2)**T.
15: * WITH DPARAM(1)=DFLAG, H HAS ONE OF THE FOLLOWING FORMS..
16: *
17: * DFLAG=-1.D0 DFLAG=0.D0 DFLAG=1.D0 DFLAG=-2.D0
18: *
19: * (DH11 DH12) (1.D0 DH12) (DH11 1.D0) (1.D0 0.D0)
20: * H=( ) ( ) ( ) ( )
21: * (DH21 DH22), (DH21 1.D0), (-1.D0 DH22), (0.D0 1.D0).
22: * LOCATIONS 2-4 OF DPARAM CONTAIN DH11, DH21, DH12, AND DH22
23: * RESPECTIVELY. (VALUES OF 1.D0, -1.D0, OR 0.D0 IMPLIED BY THE
24: * VALUE OF DPARAM(1) ARE NOT STORED IN DPARAM.)
25: *
26: * THE VALUES OF GAMSQ AND RGAMSQ SET IN THE DATA STATEMENT MAY BE
27: * INEXACT. THIS IS OK AS THEY ARE ONLY USED FOR TESTING THE SIZE
28: * OF DD1 AND DD2. ALL ACTUAL SCALING OF DATA IS DONE USING GAM.
29: *
30: *
31: * Arguments
32: * =========
33: *
34: * DD1 (input/output) DOUBLE PRECISION
35: *
36: * DD2 (input/output) DOUBLE PRECISION
37: *
38: * DX1 (input/output) DOUBLE PRECISION
39: *
40: * DY1 (input) DOUBLE PRECISION
41: *
42: * DPARAM (input/output) DOUBLE PRECISION array, dimension 5
43: * DPARAM(1)=DFLAG
44: * DPARAM(2)=DH11
45: * DPARAM(3)=DH21
46: * DPARAM(4)=DH12
47: * DPARAM(5)=DH22
48: *
49: * =====================================================================
50: *
51: * .. Local Scalars ..
52: DOUBLE PRECISION DFLAG,DH11,DH12,DH21,DH22,DP1,DP2,DQ1,DQ2,DTEMP,
53: + DU,GAM,GAMSQ,ONE,RGAMSQ,TWO,ZERO
54: INTEGER IGO
55: * ..
56: * .. Intrinsic Functions ..
57: INTRINSIC DABS
58: * ..
59: * .. Data statements ..
60: *
61: DATA ZERO,ONE,TWO/0.D0,1.D0,2.D0/
62: DATA GAM,GAMSQ,RGAMSQ/4096.D0,16777216.D0,5.9604645D-8/
63: * ..
64:
65: IF (.NOT.DD1.LT.ZERO) GO TO 10
66: * GO ZERO-H-D-AND-DX1..
67: GO TO 60
68: 10 CONTINUE
69: * CASE-DD1-NONNEGATIVE
70: DP2 = DD2*DY1
71: IF (.NOT.DP2.EQ.ZERO) GO TO 20
72: DFLAG = -TWO
73: GO TO 260
74: 20 CONTINUE
75: * REGULAR-CASE..
76: DP1 = DD1*DX1
77: DQ2 = DP2*DY1
78: DQ1 = DP1*DX1
79: *
80: IF (.NOT.DABS(DQ1).GT.DABS(DQ2)) GO TO 40
81: DH21 = -DY1/DX1
82: DH12 = DP2/DP1
83: *
84: DU = ONE - DH12*DH21
85: *
86: IF (.NOT.DU.LE.ZERO) GO TO 30
87: * GO ZERO-H-D-AND-DX1..
88: GO TO 60
89: 30 CONTINUE
90: DFLAG = ZERO
91: DD1 = DD1/DU
92: DD2 = DD2/DU
93: DX1 = DX1*DU
94: * GO SCALE-CHECK..
95: GO TO 100
96: 40 CONTINUE
97: IF (.NOT.DQ2.LT.ZERO) GO TO 50
98: * GO ZERO-H-D-AND-DX1..
99: GO TO 60
100: 50 CONTINUE
101: DFLAG = ONE
102: DH11 = DP1/DP2
103: DH22 = DX1/DY1
104: DU = ONE + DH11*DH22
105: DTEMP = DD2/DU
106: DD2 = DD1/DU
107: DD1 = DTEMP
108: DX1 = DY1*DU
109: * GO SCALE-CHECK
110: GO TO 100
111: 60 CONTINUE
112: * PROCEDURE..ZERO-H-D-AND-DX1..
113: DFLAG = -ONE
114: DH11 = ZERO
115: DH12 = ZERO
116: DH21 = ZERO
117: DH22 = ZERO
118: *
119: DD1 = ZERO
120: DD2 = ZERO
121: DX1 = ZERO
122: * RETURN..
123: GO TO 220
124: 70 CONTINUE
125: * PROCEDURE..FIX-H..
126: IF (.NOT.DFLAG.GE.ZERO) GO TO 90
127: *
128: IF (.NOT.DFLAG.EQ.ZERO) GO TO 80
129: DH11 = ONE
130: DH22 = ONE
131: DFLAG = -ONE
132: GO TO 90
133: 80 CONTINUE
134: DH21 = -ONE
135: DH12 = ONE
136: DFLAG = -ONE
137: 90 CONTINUE
138: GO TO (150,180,210) IGO
139: GO TO 120
140: 100 CONTINUE
141: * PROCEDURE..SCALE-CHECK
142: 110 CONTINUE
143: IF (.NOT.DD1.LE.RGAMSQ) GO TO 130
144: IF (DD1.EQ.ZERO) GO TO 160
145: IGO = 0
146: * FIX-H..
147: GO TO 70
148: 120 CONTINUE
149: DD1 = DD1*GAM**2
150: DX1 = DX1/GAM
151: DH11 = DH11/GAM
152: DH12 = DH12/GAM
153: GO TO 110
154: 130 CONTINUE
155: 140 CONTINUE
156: IF (.NOT.DD1.GE.GAMSQ) GO TO 160
157: IGO = 1
158: * FIX-H..
159: GO TO 70
160: 150 CONTINUE
161: DD1 = DD1/GAM**2
162: DX1 = DX1*GAM
163: DH11 = DH11*GAM
164: DH12 = DH12*GAM
165: GO TO 140
166: 160 CONTINUE
167: 170 CONTINUE
168: IF (.NOT.DABS(DD2).LE.RGAMSQ) GO TO 190
169: IF (DD2.EQ.ZERO) GO TO 220
170: IGO = 2
171: * FIX-H..
172: GO TO 70
173: 180 CONTINUE
174: DD2 = DD2*GAM**2
175: DH21 = DH21/GAM
176: DH22 = DH22/GAM
177: GO TO 170
178: 190 CONTINUE
179: 200 CONTINUE
180: IF (.NOT.DABS(DD2).GE.GAMSQ) GO TO 220
181: IGO = 3
182: * FIX-H..
183: GO TO 70
184: 210 CONTINUE
185: DD2 = DD2/GAM**2
186: DH21 = DH21*GAM
187: DH22 = DH22*GAM
188: GO TO 200
189: 220 CONTINUE
190: IF (DFLAG.LT.ZERO) THEN
191: GO TO 250
192: ELSE IF (DFLAG.EQ.ZERO) THEN
193: GO TO 230
194: ELSE
195: GO TO 240
196: END IF
197: 230 CONTINUE
198: DPARAM(3) = DH21
199: DPARAM(4) = DH12
200: GO TO 260
201: 240 CONTINUE
202: DPARAM(2) = DH11
203: DPARAM(5) = DH22
204: GO TO 260
205: 250 CONTINUE
206: DPARAM(2) = DH11
207: DPARAM(3) = DH21
208: DPARAM(4) = DH12
209: DPARAM(5) = DH22
210: 260 CONTINUE
211: DPARAM(1) = DFLAG
212: RETURN
213: END
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