Annotation of rpl/lapack/lapack/ztrexc.f, revision 1.11
1.8 bertrand 1: *> \brief \b ZTREXC
2: *
3: * =========== DOCUMENTATION ===========
4: *
5: * Online html documentation available at
6: * http://www.netlib.org/lapack/explore-html/
7: *
8: *> \htmlonly
9: *> Download ZTREXC + dependencies
10: *> <a href="http://www.netlib.org/cgi-bin/netlibfiles.tgz?format=tgz&filename=/lapack/lapack_routine/ztrexc.f">
11: *> [TGZ]</a>
12: *> <a href="http://www.netlib.org/cgi-bin/netlibfiles.zip?format=zip&filename=/lapack/lapack_routine/ztrexc.f">
13: *> [ZIP]</a>
14: *> <a href="http://www.netlib.org/cgi-bin/netlibfiles.txt?format=txt&filename=/lapack/lapack_routine/ztrexc.f">
15: *> [TXT]</a>
16: *> \endhtmlonly
17: *
18: * Definition:
19: * ===========
20: *
21: * SUBROUTINE ZTREXC( COMPQ, N, T, LDT, Q, LDQ, IFST, ILST, INFO )
22: *
23: * .. Scalar Arguments ..
24: * CHARACTER COMPQ
25: * INTEGER IFST, ILST, INFO, LDQ, LDT, N
26: * ..
27: * .. Array Arguments ..
28: * COMPLEX*16 Q( LDQ, * ), T( LDT, * )
29: * ..
30: *
31: *
32: *> \par Purpose:
33: * =============
34: *>
35: *> \verbatim
36: *>
37: *> ZTREXC reorders the Schur factorization of a complex matrix
38: *> A = Q*T*Q**H, so that the diagonal element of T with row index IFST
39: *> is moved to row ILST.
40: *>
41: *> The Schur form T is reordered by a unitary similarity transformation
42: *> Z**H*T*Z, and optionally the matrix Q of Schur vectors is updated by
43: *> postmultplying it with Z.
44: *> \endverbatim
45: *
46: * Arguments:
47: * ==========
48: *
49: *> \param[in] COMPQ
50: *> \verbatim
51: *> COMPQ is CHARACTER*1
52: *> = 'V': update the matrix Q of Schur vectors;
53: *> = 'N': do not update Q.
54: *> \endverbatim
55: *>
56: *> \param[in] N
57: *> \verbatim
58: *> N is INTEGER
59: *> The order of the matrix T. N >= 0.
60: *> \endverbatim
61: *>
62: *> \param[in,out] T
63: *> \verbatim
64: *> T is COMPLEX*16 array, dimension (LDT,N)
65: *> On entry, the upper triangular matrix T.
66: *> On exit, the reordered upper triangular matrix.
67: *> \endverbatim
68: *>
69: *> \param[in] LDT
70: *> \verbatim
71: *> LDT is INTEGER
72: *> The leading dimension of the array T. LDT >= max(1,N).
73: *> \endverbatim
74: *>
75: *> \param[in,out] Q
76: *> \verbatim
77: *> Q is COMPLEX*16 array, dimension (LDQ,N)
78: *> On entry, if COMPQ = 'V', the matrix Q of Schur vectors.
79: *> On exit, if COMPQ = 'V', Q has been postmultiplied by the
80: *> unitary transformation matrix Z which reorders T.
81: *> If COMPQ = 'N', Q is not referenced.
82: *> \endverbatim
83: *>
84: *> \param[in] LDQ
85: *> \verbatim
86: *> LDQ is INTEGER
87: *> The leading dimension of the array Q. LDQ >= max(1,N).
88: *> \endverbatim
89: *>
90: *> \param[in] IFST
91: *> \verbatim
92: *> IFST is INTEGER
93: *> \endverbatim
94: *>
95: *> \param[in] ILST
96: *> \verbatim
97: *> ILST is INTEGER
98: *>
99: *> Specify the reordering of the diagonal elements of T:
100: *> The element with row index IFST is moved to row ILST by a
101: *> sequence of transpositions between adjacent elements.
102: *> 1 <= IFST <= N; 1 <= ILST <= N.
103: *> \endverbatim
104: *>
105: *> \param[out] INFO
106: *> \verbatim
107: *> INFO is INTEGER
108: *> = 0: successful exit
109: *> < 0: if INFO = -i, the i-th argument had an illegal value
110: *> \endverbatim
111: *
112: * Authors:
113: * ========
114: *
115: *> \author Univ. of Tennessee
116: *> \author Univ. of California Berkeley
117: *> \author Univ. of Colorado Denver
118: *> \author NAG Ltd.
119: *
120: *> \date November 2011
121: *
122: *> \ingroup complex16OTHERcomputational
123: *
124: * =====================================================================
1.1 bertrand 125: SUBROUTINE ZTREXC( COMPQ, N, T, LDT, Q, LDQ, IFST, ILST, INFO )
126: *
1.8 bertrand 127: * -- LAPACK computational routine (version 3.4.0) --
1.1 bertrand 128: * -- LAPACK is a software package provided by Univ. of Tennessee, --
129: * -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
1.8 bertrand 130: * November 2011
1.1 bertrand 131: *
132: * .. Scalar Arguments ..
133: CHARACTER COMPQ
134: INTEGER IFST, ILST, INFO, LDQ, LDT, N
135: * ..
136: * .. Array Arguments ..
137: COMPLEX*16 Q( LDQ, * ), T( LDT, * )
138: * ..
139: *
140: * =====================================================================
141: *
142: * .. Local Scalars ..
143: LOGICAL WANTQ
144: INTEGER K, M1, M2, M3
145: DOUBLE PRECISION CS
146: COMPLEX*16 SN, T11, T22, TEMP
147: * ..
148: * .. External Functions ..
149: LOGICAL LSAME
150: EXTERNAL LSAME
151: * ..
152: * .. External Subroutines ..
153: EXTERNAL XERBLA, ZLARTG, ZROT
154: * ..
155: * .. Intrinsic Functions ..
156: INTRINSIC DCONJG, MAX
157: * ..
158: * .. Executable Statements ..
159: *
160: * Decode and test the input parameters.
161: *
162: INFO = 0
163: WANTQ = LSAME( COMPQ, 'V' )
164: IF( .NOT.LSAME( COMPQ, 'N' ) .AND. .NOT.WANTQ ) THEN
165: INFO = -1
166: ELSE IF( N.LT.0 ) THEN
167: INFO = -2
168: ELSE IF( LDT.LT.MAX( 1, N ) ) THEN
169: INFO = -4
170: ELSE IF( LDQ.LT.1 .OR. ( WANTQ .AND. LDQ.LT.MAX( 1, N ) ) ) THEN
171: INFO = -6
172: ELSE IF( IFST.LT.1 .OR. IFST.GT.N ) THEN
173: INFO = -7
174: ELSE IF( ILST.LT.1 .OR. ILST.GT.N ) THEN
175: INFO = -8
176: END IF
177: IF( INFO.NE.0 ) THEN
178: CALL XERBLA( 'ZTREXC', -INFO )
179: RETURN
180: END IF
181: *
182: * Quick return if possible
183: *
184: IF( N.EQ.1 .OR. IFST.EQ.ILST )
185: $ RETURN
186: *
187: IF( IFST.LT.ILST ) THEN
188: *
189: * Move the IFST-th diagonal element forward down the diagonal.
190: *
191: M1 = 0
192: M2 = -1
193: M3 = 1
194: ELSE
195: *
196: * Move the IFST-th diagonal element backward up the diagonal.
197: *
198: M1 = -1
199: M2 = 0
200: M3 = -1
201: END IF
202: *
203: DO 10 K = IFST + M1, ILST + M2, M3
204: *
205: * Interchange the k-th and (k+1)-th diagonal elements.
206: *
207: T11 = T( K, K )
208: T22 = T( K+1, K+1 )
209: *
210: * Determine the transformation to perform the interchange.
211: *
212: CALL ZLARTG( T( K, K+1 ), T22-T11, CS, SN, TEMP )
213: *
214: * Apply transformation to the matrix T.
215: *
216: IF( K+2.LE.N )
217: $ CALL ZROT( N-K-1, T( K, K+2 ), LDT, T( K+1, K+2 ), LDT, CS,
218: $ SN )
219: CALL ZROT( K-1, T( 1, K ), 1, T( 1, K+1 ), 1, CS,
220: $ DCONJG( SN ) )
221: *
222: T( K, K ) = T22
223: T( K+1, K+1 ) = T11
224: *
225: IF( WANTQ ) THEN
226: *
227: * Accumulate transformation in the matrix Q.
228: *
229: CALL ZROT( N, Q( 1, K ), 1, Q( 1, K+1 ), 1, CS,
230: $ DCONJG( SN ) )
231: END IF
232: *
233: 10 CONTINUE
234: *
235: RETURN
236: *
237: * End of ZTREXC
238: *
239: END
CVSweb interface <joel.bertrand@systella.fr>
![[BACK]](/cvsweb/icons/back.gif){kind=icon}
Return to ztrexc.f CVS log ![[TXT]](/cvsweb/icons/text.gif){kind=icon}
![[DIR]](/cvsweb/icons/dir.gif){kind=icon}
Up to [local] / rpl / lapack / lapack