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zla_gbrcond_c.f
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1 *> \brief \b ZLA_GBRCOND_C computes the infinity norm condition number of op(A)*inv(diag(c)) for general banded matrices.
2 *
3 * =========== DOCUMENTATION ===========
4 *
5 * Online html documentation available at
6 * http://www.netlib.org/lapack/explore-html/
7 *
8 *> \htmlonly
9 *> Download ZLA_GBRCOND_C + dependencies
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11 *> [TGZ]</a>
12 *> <a href="http://www.netlib.org/cgi-bin/netlibfiles.zip?format=zip&filename=/lapack/lapack_routine/zla_gbrcond_c.f">
13 *> [ZIP]</a>
14 *> <a href="http://www.netlib.org/cgi-bin/netlibfiles.txt?format=txt&filename=/lapack/lapack_routine/zla_gbrcond_c.f">
15 *> [TXT]</a>
16 *> \endhtmlonly
17 *
18 * Definition:
19 * ===========
20 *
21 * DOUBLE PRECISION FUNCTION ZLA_GBRCOND_C( TRANS, N, KL, KU, AB,
22 * LDAB, AFB, LDAFB, IPIV,
23 * C, CAPPLY, INFO, WORK,
24 * RWORK )
25 *
26 * .. Scalar Arguments ..
27 * CHARACTER TRANS
28 * LOGICAL CAPPLY
29 * INTEGER N, KL, KU, KD, KE, LDAB, LDAFB, INFO
30 * ..
31 * .. Array Arguments ..
32 * INTEGER IPIV( * )
33 * COMPLEX*16 AB( LDAB, * ), AFB( LDAFB, * ), WORK( * )
34 * DOUBLE PRECISION C( * ), RWORK( * )
35 *
36 *
37 *
38 *> \par Purpose:
39 * =============
40 *>
41 *> \verbatim
42 *>
43 *> ZLA_GBRCOND_C Computes the infinity norm condition number of
44 *> op(A) * inv(diag(C)) where C is a DOUBLE PRECISION vector.
45 *> \endverbatim
46 *
47 * Arguments:
48 * ==========
49 *
50 *> \param[in] TRANS
51 *> \verbatim
52 *> TRANS is CHARACTER*1
53 *> Specifies the form of the system of equations:
54 *> = 'N': A * X = B (No transpose)
55 *> = 'T': A**T * X = B (Transpose)
56 *> = 'C': A**H * X = B (Conjugate Transpose = Transpose)
57 *> \endverbatim
58 *>
59 *> \param[in] N
60 *> \verbatim
61 *> N is INTEGER
62 *> The number of linear equations, i.e., the order of the
63 *> matrix A. N >= 0.
64 *> \endverbatim
65 *>
66 *> \param[in] KL
67 *> \verbatim
68 *> KL is INTEGER
69 *> The number of subdiagonals within the band of A. KL >= 0.
70 *> \endverbatim
71 *>
72 *> \param[in] KU
73 *> \verbatim
74 *> KU is INTEGER
75 *> The number of superdiagonals within the band of A. KU >= 0.
76 *> \endverbatim
77 *>
78 *> \param[in] AB
79 *> \verbatim
80 *> AB is COMPLEX*16 array, dimension (LDAB,N)
81 *> On entry, the matrix A in band storage, in rows 1 to KL+KU+1.
82 *> The j-th column of A is stored in the j-th column of the
83 *> array AB as follows:
84 *> AB(KU+1+i-j,j) = A(i,j) for max(1,j-KU)<=i<=min(N,j+kl)
85 *> \endverbatim
86 *>
87 *> \param[in] LDAB
88 *> \verbatim
89 *> LDAB is INTEGER
90 *> The leading dimension of the array AB. LDAB >= KL+KU+1.
91 *> \endverbatim
92 *>
93 *> \param[in] AFB
94 *> \verbatim
95 *> AFB is COMPLEX*16 array, dimension (LDAFB,N)
96 *> Details of the LU factorization of the band matrix A, as
97 *> computed by ZGBTRF. U is stored as an upper triangular
98 *> band matrix with KL+KU superdiagonals in rows 1 to KL+KU+1,
99 *> and the multipliers used during the factorization are stored
100 *> in rows KL+KU+2 to 2*KL+KU+1.
101 *> \endverbatim
102 *>
103 *> \param[in] LDAFB
104 *> \verbatim
105 *> LDAFB is INTEGER
106 *> The leading dimension of the array AFB. LDAFB >= 2*KL+KU+1.
107 *> \endverbatim
108 *>
109 *> \param[in] IPIV
110 *> \verbatim
111 *> IPIV is INTEGER array, dimension (N)
112 *> The pivot indices from the factorization A = P*L*U
113 *> as computed by ZGBTRF; row i of the matrix was interchanged
114 *> with row IPIV(i).
115 *> \endverbatim
116 *>
117 *> \param[in] C
118 *> \verbatim
119 *> C is DOUBLE PRECISION array, dimension (N)
120 *> The vector C in the formula op(A) * inv(diag(C)).
121 *> \endverbatim
122 *>
123 *> \param[in] CAPPLY
124 *> \verbatim
125 *> CAPPLY is LOGICAL
126 *> If .TRUE. then access the vector C in the formula above.
127 *> \endverbatim
128 *>
129 *> \param[out] INFO
130 *> \verbatim
131 *> INFO is INTEGER
132 *> = 0: Successful exit.
133 *> i > 0: The ith argument is invalid.
134 *> \endverbatim
135 *>
136 *> \param[in] WORK
137 *> \verbatim
138 *> WORK is COMPLEX*16 array, dimension (2*N).
139 *> Workspace.
140 *> \endverbatim
141 *>
142 *> \param[in] RWORK
143 *> \verbatim
144 *> RWORK is DOUBLE PRECISION array, dimension (N).
145 *> Workspace.
146 *> \endverbatim
147 *
148 * Authors:
149 * ========
150 *
151 *> \author Univ. of Tennessee
152 *> \author Univ. of California Berkeley
153 *> \author Univ. of Colorado Denver
154 *> \author NAG Ltd.
155 *
156 *> \date September 2012
157 *
158 *> \ingroup complex16GBcomputational
159 *
160 * =====================================================================
161  DOUBLE PRECISION FUNCTION zla_gbrcond_c( TRANS, N, KL, KU, AB,
162  $ ldab, afb, ldafb, ipiv,
163  $ c, capply, info, work,
164  $ rwork )
165 *
166 * -- LAPACK computational routine (version 3.4.2) --
167 * -- LAPACK is a software package provided by Univ. of Tennessee, --
168 * -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
169 * September 2012
170 *
171 * .. Scalar Arguments ..
172  CHARACTER trans
173  LOGICAL capply
174  INTEGER n, kl, ku, kd, ke, ldab, ldafb, info
175 * ..
176 * .. Array Arguments ..
177  INTEGER ipiv( * )
178  COMPLEX*16 ab( ldab, * ), afb( ldafb, * ), work( * )
179  DOUBLE PRECISION c( * ), rwork( * )
180 *
181 *
182 * =====================================================================
183 *
184 * .. Local Scalars ..
185  LOGICAL notrans
186  INTEGER kase, i, j
187  DOUBLE PRECISION ainvnm, anorm, tmp
188  COMPLEX*16 zdum
189 * ..
190 * .. Local Arrays ..
191  INTEGER isave( 3 )
192 * ..
193 * .. External Functions ..
194  LOGICAL lsame
195  EXTERNAL lsame
196 * ..
197 * .. External Subroutines ..
198  EXTERNAL zlacn2, zgbtrs, xerbla
199 * ..
200 * .. Intrinsic Functions ..
201  INTRINSIC abs, max
202 * ..
203 * .. Statement Functions ..
204  DOUBLE PRECISION cabs1
205 * ..
206 * .. Statement Function Definitions ..
207  cabs1( zdum ) = abs( dble( zdum ) ) + abs( dimag( zdum ) )
208 * ..
209 * .. Executable Statements ..
210  zla_gbrcond_c = 0.0d+0
211 *
212  info = 0
213  notrans = lsame( trans, 'N' )
214  IF ( .NOT. notrans .AND. .NOT. lsame( trans, 'T' ) .AND. .NOT.
215  $ lsame( trans, 'C' ) ) THEN
216  info = -1
217  ELSE IF( n.LT.0 ) THEN
218  info = -2
219  ELSE IF( kl.LT.0 .OR. kl.GT.n-1 ) THEN
220  info = -3
221  ELSE IF( ku.LT.0 .OR. ku.GT.n-1 ) THEN
222  info = -4
223  ELSE IF( ldab.LT.kl+ku+1 ) THEN
224  info = -6
225  ELSE IF( ldafb.LT.2*kl+ku+1 ) THEN
226  info = -8
227  END IF
228  IF( info.NE.0 ) THEN
229  CALL xerbla( 'ZLA_GBRCOND_C', -info )
230  RETURN
231  END IF
232 *
233 * Compute norm of op(A)*op2(C).
234 *
235  anorm = 0.0d+0
236  kd = ku + 1
237  ke = kl + 1
238  IF ( notrans ) THEN
239  DO i = 1, n
240  tmp = 0.0d+0
241  IF ( capply ) THEN
242  DO j = max( i-kl, 1 ), min( i+ku, n )
243  tmp = tmp + cabs1( ab( kd+i-j, j ) ) / c( j )
244  END DO
245  ELSE
246  DO j = max( i-kl, 1 ), min( i+ku, n )
247  tmp = tmp + cabs1( ab( kd+i-j, j ) )
248  END DO
249  END IF
250  rwork( i ) = tmp
251  anorm = max( anorm, tmp )
252  END DO
253  ELSE
254  DO i = 1, n
255  tmp = 0.0d+0
256  IF ( capply ) THEN
257  DO j = max( i-kl, 1 ), min( i+ku, n )
258  tmp = tmp + cabs1( ab( ke-i+j, i ) ) / c( j )
259  END DO
260  ELSE
261  DO j = max( i-kl, 1 ), min( i+ku, n )
262  tmp = tmp + cabs1( ab( ke-i+j, i ) )
263  END DO
264  END IF
265  rwork( i ) = tmp
266  anorm = max( anorm, tmp )
267  END DO
268  END IF
269 *
270 * Quick return if possible.
271 *
272  IF( n.EQ.0 ) THEN
273  zla_gbrcond_c = 1.0d+0
274  RETURN
275  ELSE IF( anorm .EQ. 0.0d+0 ) THEN
276  RETURN
277  END IF
278 *
279 * Estimate the norm of inv(op(A)).
280 *
281  ainvnm = 0.0d+0
282 *
283  kase = 0
284  10 CONTINUE
285  CALL zlacn2( n, work( n+1 ), work, ainvnm, kase, isave )
286  IF( kase.NE.0 ) THEN
287  IF( kase.EQ.2 ) THEN
288 *
289 * Multiply by R.
290 *
291  DO i = 1, n
292  work( i ) = work( i ) * rwork( i )
293  END DO
294 *
295  IF ( notrans ) THEN
296  CALL zgbtrs( 'No transpose', n, kl, ku, 1, afb, ldafb,
297  $ ipiv, work, n, info )
298  ELSE
299  CALL zgbtrs( 'Conjugate transpose', n, kl, ku, 1, afb,
300  $ ldafb, ipiv, work, n, info )
301  ENDIF
302 *
303 * Multiply by inv(C).
304 *
305  IF ( capply ) THEN
306  DO i = 1, n
307  work( i ) = work( i ) * c( i )
308  END DO
309  END IF
310  ELSE
311 *
312 * Multiply by inv(C**H).
313 *
314  IF ( capply ) THEN
315  DO i = 1, n
316  work( i ) = work( i ) * c( i )
317  END DO
318  END IF
319 *
320  IF ( notrans ) THEN
321  CALL zgbtrs( 'Conjugate transpose', n, kl, ku, 1, afb,
322  $ ldafb, ipiv, work, n, info )
323  ELSE
324  CALL zgbtrs( 'No transpose', n, kl, ku, 1, afb, ldafb,
325  $ ipiv, work, n, info )
326  END IF
327 *
328 * Multiply by R.
329 *
330  DO i = 1, n
331  work( i ) = work( i ) * rwork( i )
332  END DO
333  END IF
334  go to 10
335  END IF
336 *
337 * Compute the estimate of the reciprocal condition number.
338 *
339  IF( ainvnm .NE. 0.0d+0 )
340  $ zla_gbrcond_c = 1.0d+0 / ainvnm
341 *
342  RETURN
343 *
344  END