Annotation of rpl/lapack/lapack/dlasd7.f, revision 1.5
1.1 bertrand 1: SUBROUTINE DLASD7( ICOMPQ, NL, NR, SQRE, K, D, Z, ZW, VF, VFW, VL,
2: $ VLW, ALPHA, BETA, DSIGMA, IDX, IDXP, IDXQ,
3: $ PERM, GIVPTR, GIVCOL, LDGCOL, GIVNUM, LDGNUM,
4: $ C, S, INFO )
5: *
6: * -- LAPACK auxiliary routine (version 3.2) --
7: * -- LAPACK is a software package provided by Univ. of Tennessee, --
8: * -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
9: * November 2006
10: *
11: * .. Scalar Arguments ..
12: INTEGER GIVPTR, ICOMPQ, INFO, K, LDGCOL, LDGNUM, NL,
13: $ NR, SQRE
14: DOUBLE PRECISION ALPHA, BETA, C, S
15: * ..
16: * .. Array Arguments ..
17: INTEGER GIVCOL( LDGCOL, * ), IDX( * ), IDXP( * ),
18: $ IDXQ( * ), PERM( * )
19: DOUBLE PRECISION D( * ), DSIGMA( * ), GIVNUM( LDGNUM, * ),
20: $ VF( * ), VFW( * ), VL( * ), VLW( * ), Z( * ),
21: $ ZW( * )
22: * ..
23: *
24: * Purpose
25: * =======
26: *
27: * DLASD7 merges the two sets of singular values together into a single
28: * sorted set. Then it tries to deflate the size of the problem. There
29: * are two ways in which deflation can occur: when two or more singular
30: * values are close together or if there is a tiny entry in the Z
31: * vector. For each such occurrence the order of the related
32: * secular equation problem is reduced by one.
33: *
34: * DLASD7 is called from DLASD6.
35: *
36: * Arguments
37: * =========
38: *
39: * ICOMPQ (input) INTEGER
40: * Specifies whether singular vectors are to be computed
41: * in compact form, as follows:
42: * = 0: Compute singular values only.
43: * = 1: Compute singular vectors of upper
44: * bidiagonal matrix in compact form.
45: *
46: * NL (input) INTEGER
47: * The row dimension of the upper block. NL >= 1.
48: *
49: * NR (input) INTEGER
50: * The row dimension of the lower block. NR >= 1.
51: *
52: * SQRE (input) INTEGER
53: * = 0: the lower block is an NR-by-NR square matrix.
54: * = 1: the lower block is an NR-by-(NR+1) rectangular matrix.
55: *
56: * The bidiagonal matrix has
57: * N = NL + NR + 1 rows and
58: * M = N + SQRE >= N columns.
59: *
60: * K (output) INTEGER
61: * Contains the dimension of the non-deflated matrix, this is
62: * the order of the related secular equation. 1 <= K <=N.
63: *
64: * D (input/output) DOUBLE PRECISION array, dimension ( N )
65: * On entry D contains the singular values of the two submatrices
66: * to be combined. On exit D contains the trailing (N-K) updated
67: * singular values (those which were deflated) sorted into
68: * increasing order.
69: *
70: * Z (output) DOUBLE PRECISION array, dimension ( M )
71: * On exit Z contains the updating row vector in the secular
72: * equation.
73: *
74: * ZW (workspace) DOUBLE PRECISION array, dimension ( M )
75: * Workspace for Z.
76: *
77: * VF (input/output) DOUBLE PRECISION array, dimension ( M )
78: * On entry, VF(1:NL+1) contains the first components of all
79: * right singular vectors of the upper block; and VF(NL+2:M)
80: * contains the first components of all right singular vectors
81: * of the lower block. On exit, VF contains the first components
82: * of all right singular vectors of the bidiagonal matrix.
83: *
84: * VFW (workspace) DOUBLE PRECISION array, dimension ( M )
85: * Workspace for VF.
86: *
87: * VL (input/output) DOUBLE PRECISION array, dimension ( M )
88: * On entry, VL(1:NL+1) contains the last components of all
89: * right singular vectors of the upper block; and VL(NL+2:M)
90: * contains the last components of all right singular vectors
91: * of the lower block. On exit, VL contains the last components
92: * of all right singular vectors of the bidiagonal matrix.
93: *
94: * VLW (workspace) DOUBLE PRECISION array, dimension ( M )
95: * Workspace for VL.
96: *
97: * ALPHA (input) DOUBLE PRECISION
98: * Contains the diagonal element associated with the added row.
99: *
100: * BETA (input) DOUBLE PRECISION
101: * Contains the off-diagonal element associated with the added
102: * row.
103: *
104: * DSIGMA (output) DOUBLE PRECISION array, dimension ( N )
105: * Contains a copy of the diagonal elements (K-1 singular values
106: * and one zero) in the secular equation.
107: *
108: * IDX (workspace) INTEGER array, dimension ( N )
109: * This will contain the permutation used to sort the contents of
110: * D into ascending order.
111: *
112: * IDXP (workspace) INTEGER array, dimension ( N )
113: * This will contain the permutation used to place deflated
114: * values of D at the end of the array. On output IDXP(2:K)
115: * points to the nondeflated D-values and IDXP(K+1:N)
116: * points to the deflated singular values.
117: *
118: * IDXQ (input) INTEGER array, dimension ( N )
119: * This contains the permutation which separately sorts the two
120: * sub-problems in D into ascending order. Note that entries in
121: * the first half of this permutation must first be moved one
122: * position backward; and entries in the second half
123: * must first have NL+1 added to their values.
124: *
125: * PERM (output) INTEGER array, dimension ( N )
126: * The permutations (from deflation and sorting) to be applied
127: * to each singular block. Not referenced if ICOMPQ = 0.
128: *
129: * GIVPTR (output) INTEGER
130: * The number of Givens rotations which took place in this
131: * subproblem. Not referenced if ICOMPQ = 0.
132: *
133: * GIVCOL (output) INTEGER array, dimension ( LDGCOL, 2 )
134: * Each pair of numbers indicates a pair of columns to take place
135: * in a Givens rotation. Not referenced if ICOMPQ = 0.
136: *
137: * LDGCOL (input) INTEGER
138: * The leading dimension of GIVCOL, must be at least N.
139: *
140: * GIVNUM (output) DOUBLE PRECISION array, dimension ( LDGNUM, 2 )
141: * Each number indicates the C or S value to be used in the
142: * corresponding Givens rotation. Not referenced if ICOMPQ = 0.
143: *
144: * LDGNUM (input) INTEGER
145: * The leading dimension of GIVNUM, must be at least N.
146: *
147: * C (output) DOUBLE PRECISION
148: * C contains garbage if SQRE =0 and the C-value of a Givens
149: * rotation related to the right null space if SQRE = 1.
150: *
151: * S (output) DOUBLE PRECISION
152: * S contains garbage if SQRE =0 and the S-value of a Givens
153: * rotation related to the right null space if SQRE = 1.
154: *
155: * INFO (output) INTEGER
156: * = 0: successful exit.
157: * < 0: if INFO = -i, the i-th argument had an illegal value.
158: *
159: * Further Details
160: * ===============
161: *
162: * Based on contributions by
163: * Ming Gu and Huan Ren, Computer Science Division, University of
164: * California at Berkeley, USA
165: *
166: * =====================================================================
167: *
168: * .. Parameters ..
169: DOUBLE PRECISION ZERO, ONE, TWO, EIGHT
170: PARAMETER ( ZERO = 0.0D+0, ONE = 1.0D+0, TWO = 2.0D+0,
171: $ EIGHT = 8.0D+0 )
172: * ..
173: * .. Local Scalars ..
174: *
175: INTEGER I, IDXI, IDXJ, IDXJP, J, JP, JPREV, K2, M, N,
176: $ NLP1, NLP2
177: DOUBLE PRECISION EPS, HLFTOL, TAU, TOL, Z1
178: * ..
179: * .. External Subroutines ..
180: EXTERNAL DCOPY, DLAMRG, DROT, XERBLA
181: * ..
182: * .. External Functions ..
183: DOUBLE PRECISION DLAMCH, DLAPY2
184: EXTERNAL DLAMCH, DLAPY2
185: * ..
186: * .. Intrinsic Functions ..
187: INTRINSIC ABS, MAX
188: * ..
189: * .. Executable Statements ..
190: *
191: * Test the input parameters.
192: *
193: INFO = 0
194: N = NL + NR + 1
195: M = N + SQRE
196: *
197: IF( ( ICOMPQ.LT.0 ) .OR. ( ICOMPQ.GT.1 ) ) THEN
198: INFO = -1
199: ELSE IF( NL.LT.1 ) THEN
200: INFO = -2
201: ELSE IF( NR.LT.1 ) THEN
202: INFO = -3
203: ELSE IF( ( SQRE.LT.0 ) .OR. ( SQRE.GT.1 ) ) THEN
204: INFO = -4
205: ELSE IF( LDGCOL.LT.N ) THEN
206: INFO = -22
207: ELSE IF( LDGNUM.LT.N ) THEN
208: INFO = -24
209: END IF
210: IF( INFO.NE.0 ) THEN
211: CALL XERBLA( 'DLASD7', -INFO )
212: RETURN
213: END IF
214: *
215: NLP1 = NL + 1
216: NLP2 = NL + 2
217: IF( ICOMPQ.EQ.1 ) THEN
218: GIVPTR = 0
219: END IF
220: *
221: * Generate the first part of the vector Z and move the singular
222: * values in the first part of D one position backward.
223: *
224: Z1 = ALPHA*VL( NLP1 )
225: VL( NLP1 ) = ZERO
226: TAU = VF( NLP1 )
227: DO 10 I = NL, 1, -1
228: Z( I+1 ) = ALPHA*VL( I )
229: VL( I ) = ZERO
230: VF( I+1 ) = VF( I )
231: D( I+1 ) = D( I )
232: IDXQ( I+1 ) = IDXQ( I ) + 1
233: 10 CONTINUE
234: VF( 1 ) = TAU
235: *
236: * Generate the second part of the vector Z.
237: *
238: DO 20 I = NLP2, M
239: Z( I ) = BETA*VF( I )
240: VF( I ) = ZERO
241: 20 CONTINUE
242: *
243: * Sort the singular values into increasing order
244: *
245: DO 30 I = NLP2, N
246: IDXQ( I ) = IDXQ( I ) + NLP1
247: 30 CONTINUE
248: *
249: * DSIGMA, IDXC, IDXC, and ZW are used as storage space.
250: *
251: DO 40 I = 2, N
252: DSIGMA( I ) = D( IDXQ( I ) )
253: ZW( I ) = Z( IDXQ( I ) )
254: VFW( I ) = VF( IDXQ( I ) )
255: VLW( I ) = VL( IDXQ( I ) )
256: 40 CONTINUE
257: *
258: CALL DLAMRG( NL, NR, DSIGMA( 2 ), 1, 1, IDX( 2 ) )
259: *
260: DO 50 I = 2, N
261: IDXI = 1 + IDX( I )
262: D( I ) = DSIGMA( IDXI )
263: Z( I ) = ZW( IDXI )
264: VF( I ) = VFW( IDXI )
265: VL( I ) = VLW( IDXI )
266: 50 CONTINUE
267: *
268: * Calculate the allowable deflation tolerence
269: *
270: EPS = DLAMCH( 'Epsilon' )
271: TOL = MAX( ABS( ALPHA ), ABS( BETA ) )
272: TOL = EIGHT*EIGHT*EPS*MAX( ABS( D( N ) ), TOL )
273: *
274: * There are 2 kinds of deflation -- first a value in the z-vector
275: * is small, second two (or more) singular values are very close
276: * together (their difference is small).
277: *
278: * If the value in the z-vector is small, we simply permute the
279: * array so that the corresponding singular value is moved to the
280: * end.
281: *
282: * If two values in the D-vector are close, we perform a two-sided
283: * rotation designed to make one of the corresponding z-vector
284: * entries zero, and then permute the array so that the deflated
285: * singular value is moved to the end.
286: *
287: * If there are multiple singular values then the problem deflates.
288: * Here the number of equal singular values are found. As each equal
289: * singular value is found, an elementary reflector is computed to
290: * rotate the corresponding singular subspace so that the
291: * corresponding components of Z are zero in this new basis.
292: *
293: K = 1
294: K2 = N + 1
295: DO 60 J = 2, N
296: IF( ABS( Z( J ) ).LE.TOL ) THEN
297: *
298: * Deflate due to small z component.
299: *
300: K2 = K2 - 1
301: IDXP( K2 ) = J
302: IF( J.EQ.N )
303: $ GO TO 100
304: ELSE
305: JPREV = J
306: GO TO 70
307: END IF
308: 60 CONTINUE
309: 70 CONTINUE
310: J = JPREV
311: 80 CONTINUE
312: J = J + 1
313: IF( J.GT.N )
314: $ GO TO 90
315: IF( ABS( Z( J ) ).LE.TOL ) THEN
316: *
317: * Deflate due to small z component.
318: *
319: K2 = K2 - 1
320: IDXP( K2 ) = J
321: ELSE
322: *
323: * Check if singular values are close enough to allow deflation.
324: *
325: IF( ABS( D( J )-D( JPREV ) ).LE.TOL ) THEN
326: *
327: * Deflation is possible.
328: *
329: S = Z( JPREV )
330: C = Z( J )
331: *
332: * Find sqrt(a**2+b**2) without overflow or
333: * destructive underflow.
334: *
335: TAU = DLAPY2( C, S )
336: Z( J ) = TAU
337: Z( JPREV ) = ZERO
338: C = C / TAU
339: S = -S / TAU
340: *
341: * Record the appropriate Givens rotation
342: *
343: IF( ICOMPQ.EQ.1 ) THEN
344: GIVPTR = GIVPTR + 1
345: IDXJP = IDXQ( IDX( JPREV )+1 )
346: IDXJ = IDXQ( IDX( J )+1 )
347: IF( IDXJP.LE.NLP1 ) THEN
348: IDXJP = IDXJP - 1
349: END IF
350: IF( IDXJ.LE.NLP1 ) THEN
351: IDXJ = IDXJ - 1
352: END IF
353: GIVCOL( GIVPTR, 2 ) = IDXJP
354: GIVCOL( GIVPTR, 1 ) = IDXJ
355: GIVNUM( GIVPTR, 2 ) = C
356: GIVNUM( GIVPTR, 1 ) = S
357: END IF
358: CALL DROT( 1, VF( JPREV ), 1, VF( J ), 1, C, S )
359: CALL DROT( 1, VL( JPREV ), 1, VL( J ), 1, C, S )
360: K2 = K2 - 1
361: IDXP( K2 ) = JPREV
362: JPREV = J
363: ELSE
364: K = K + 1
365: ZW( K ) = Z( JPREV )
366: DSIGMA( K ) = D( JPREV )
367: IDXP( K ) = JPREV
368: JPREV = J
369: END IF
370: END IF
371: GO TO 80
372: 90 CONTINUE
373: *
374: * Record the last singular value.
375: *
376: K = K + 1
377: ZW( K ) = Z( JPREV )
378: DSIGMA( K ) = D( JPREV )
379: IDXP( K ) = JPREV
380: *
381: 100 CONTINUE
382: *
383: * Sort the singular values into DSIGMA. The singular values which
384: * were not deflated go into the first K slots of DSIGMA, except
385: * that DSIGMA(1) is treated separately.
386: *
387: DO 110 J = 2, N
388: JP = IDXP( J )
389: DSIGMA( J ) = D( JP )
390: VFW( J ) = VF( JP )
391: VLW( J ) = VL( JP )
392: 110 CONTINUE
393: IF( ICOMPQ.EQ.1 ) THEN
394: DO 120 J = 2, N
395: JP = IDXP( J )
396: PERM( J ) = IDXQ( IDX( JP )+1 )
397: IF( PERM( J ).LE.NLP1 ) THEN
398: PERM( J ) = PERM( J ) - 1
399: END IF
400: 120 CONTINUE
401: END IF
402: *
403: * The deflated singular values go back into the last N - K slots of
404: * D.
405: *
406: CALL DCOPY( N-K, DSIGMA( K+1 ), 1, D( K+1 ), 1 )
407: *
408: * Determine DSIGMA(1), DSIGMA(2), Z(1), VF(1), VL(1), VF(M), and
409: * VL(M).
410: *
411: DSIGMA( 1 ) = ZERO
412: HLFTOL = TOL / TWO
413: IF( ABS( DSIGMA( 2 ) ).LE.HLFTOL )
414: $ DSIGMA( 2 ) = HLFTOL
415: IF( M.GT.N ) THEN
416: Z( 1 ) = DLAPY2( Z1, Z( M ) )
417: IF( Z( 1 ).LE.TOL ) THEN
418: C = ONE
419: S = ZERO
420: Z( 1 ) = TOL
421: ELSE
422: C = Z1 / Z( 1 )
423: S = -Z( M ) / Z( 1 )
424: END IF
425: CALL DROT( 1, VF( M ), 1, VF( 1 ), 1, C, S )
426: CALL DROT( 1, VL( M ), 1, VL( 1 ), 1, C, S )
427: ELSE
428: IF( ABS( Z1 ).LE.TOL ) THEN
429: Z( 1 ) = TOL
430: ELSE
431: Z( 1 ) = Z1
432: END IF
433: END IF
434: *
435: * Restore Z, VF, and VL.
436: *
437: CALL DCOPY( K-1, ZW( 2 ), 1, Z( 2 ), 1 )
438: CALL DCOPY( N-1, VFW( 2 ), 1, VF( 2 ), 1 )
439: CALL DCOPY( N-1, VLW( 2 ), 1, VL( 2 ), 1 )
440: *
441: RETURN
442: *
443: * End of DLASD7
444: *
445: END
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