1: *> \brief \b DLANSP
2: *
3: * =========== DOCUMENTATION ===========
4: *
5: * Online html documentation available at
6: * http://www.netlib.org/lapack/explore-html/
7: *
8: *> \htmlonly
9: *> Download DLANSP + dependencies
10: *> <a href="http://www.netlib.org/cgi-bin/netlibfiles.tgz?format=tgz&filename=/lapack/lapack_routine/dlansp.f">
11: *> [TGZ]</a>
12: *> <a href="http://www.netlib.org/cgi-bin/netlibfiles.zip?format=zip&filename=/lapack/lapack_routine/dlansp.f">
13: *> [ZIP]</a>
14: *> <a href="http://www.netlib.org/cgi-bin/netlibfiles.txt?format=txt&filename=/lapack/lapack_routine/dlansp.f">
15: *> [TXT]</a>
16: *> \endhtmlonly
17: *
18: * Definition:
19: * ===========
20: *
21: * DOUBLE PRECISION FUNCTION DLANSP( NORM, UPLO, N, AP, WORK )
22: *
23: * .. Scalar Arguments ..
24: * CHARACTER NORM, UPLO
25: * INTEGER N
26: * ..
27: * .. Array Arguments ..
28: * DOUBLE PRECISION AP( * ), WORK( * )
29: * ..
30: *
31: *
32: *> \par Purpose:
33: * =============
34: *>
35: *> \verbatim
36: *>
37: *> DLANSP returns the value of the one norm, or the Frobenius norm, or
38: *> the infinity norm, or the element of largest absolute value of a
39: *> real symmetric matrix A, supplied in packed form.
40: *> \endverbatim
41: *>
42: *> \return DLANSP
43: *> \verbatim
44: *>
45: *> DLANSP = ( max(abs(A(i,j))), NORM = 'M' or 'm'
46: *> (
47: *> ( norm1(A), NORM = '1', 'O' or 'o'
48: *> (
49: *> ( normI(A), NORM = 'I' or 'i'
50: *> (
51: *> ( normF(A), NORM = 'F', 'f', 'E' or 'e'
52: *>
53: *> where norm1 denotes the one norm of a matrix (maximum column sum),
54: *> normI denotes the infinity norm of a matrix (maximum row sum) and
55: *> normF denotes the Frobenius norm of a matrix (square root of sum of
56: *> squares). Note that max(abs(A(i,j))) is not a consistent matrix norm.
57: *> \endverbatim
58: *
59: * Arguments:
60: * ==========
61: *
62: *> \param[in] NORM
63: *> \verbatim
64: *> NORM is CHARACTER*1
65: *> Specifies the value to be returned in DLANSP as described
66: *> above.
67: *> \endverbatim
68: *>
69: *> \param[in] UPLO
70: *> \verbatim
71: *> UPLO is CHARACTER*1
72: *> Specifies whether the upper or lower triangular part of the
73: *> symmetric matrix A is supplied.
74: *> = 'U': Upper triangular part of A is supplied
75: *> = 'L': Lower triangular part of A is supplied
76: *> \endverbatim
77: *>
78: *> \param[in] N
79: *> \verbatim
80: *> N is INTEGER
81: *> The order of the matrix A. N >= 0. When N = 0, DLANSP is
82: *> set to zero.
83: *> \endverbatim
84: *>
85: *> \param[in] AP
86: *> \verbatim
87: *> AP is DOUBLE PRECISION array, dimension (N*(N+1)/2)
88: *> The upper or lower triangle of the symmetric matrix A, packed
89: *> columnwise in a linear array. The j-th column of A is stored
90: *> in the array AP as follows:
91: *> if UPLO = 'U', AP(i + (j-1)*j/2) = A(i,j) for 1<=i<=j;
92: *> if UPLO = 'L', AP(i + (j-1)*(2n-j)/2) = A(i,j) for j<=i<=n.
93: *> \endverbatim
94: *>
95: *> \param[out] WORK
96: *> \verbatim
97: *> WORK is DOUBLE PRECISION array, dimension (MAX(1,LWORK)),
98: *> where LWORK >= N when NORM = 'I' or '1' or 'O'; otherwise,
99: *> WORK is not referenced.
100: *> \endverbatim
101: *
102: * Authors:
103: * ========
104: *
105: *> \author Univ. of Tennessee
106: *> \author Univ. of California Berkeley
107: *> \author Univ. of Colorado Denver
108: *> \author NAG Ltd.
109: *
110: *> \date November 2011
111: *
112: *> \ingroup doubleOTHERauxiliary
113: *
114: * =====================================================================
115: DOUBLE PRECISION FUNCTION DLANSP( NORM, UPLO, N, AP, WORK )
116: *
117: * -- LAPACK auxiliary routine (version 3.4.0) --
118: * -- LAPACK is a software package provided by Univ. of Tennessee, --
119: * -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
120: * November 2011
121: *
122: * .. Scalar Arguments ..
123: CHARACTER NORM, UPLO
124: INTEGER N
125: * ..
126: * .. Array Arguments ..
127: DOUBLE PRECISION AP( * ), WORK( * )
128: * ..
129: *
130: * =====================================================================
131: *
132: * .. Parameters ..
133: DOUBLE PRECISION ONE, ZERO
134: PARAMETER ( ONE = 1.0D+0, ZERO = 0.0D+0 )
135: * ..
136: * .. Local Scalars ..
137: INTEGER I, J, K
138: DOUBLE PRECISION ABSA, SCALE, SUM, VALUE
139: * ..
140: * .. External Subroutines ..
141: EXTERNAL DLASSQ
142: * ..
143: * .. External Functions ..
144: LOGICAL LSAME
145: EXTERNAL LSAME
146: * ..
147: * .. Intrinsic Functions ..
148: INTRINSIC ABS, MAX, SQRT
149: * ..
150: * .. Executable Statements ..
151: *
152: IF( N.EQ.0 ) THEN
153: VALUE = ZERO
154: ELSE IF( LSAME( NORM, 'M' ) ) THEN
155: *
156: * Find max(abs(A(i,j))).
157: *
158: VALUE = ZERO
159: IF( LSAME( UPLO, 'U' ) ) THEN
160: K = 1
161: DO 20 J = 1, N
162: DO 10 I = K, K + J - 1
163: VALUE = MAX( VALUE, ABS( AP( I ) ) )
164: 10 CONTINUE
165: K = K + J
166: 20 CONTINUE
167: ELSE
168: K = 1
169: DO 40 J = 1, N
170: DO 30 I = K, K + N - J
171: VALUE = MAX( VALUE, ABS( AP( I ) ) )
172: 30 CONTINUE
173: K = K + N - J + 1
174: 40 CONTINUE
175: END IF
176: ELSE IF( ( LSAME( NORM, 'I' ) ) .OR. ( LSAME( NORM, 'O' ) ) .OR.
177: $ ( NORM.EQ.'1' ) ) THEN
178: *
179: * Find normI(A) ( = norm1(A), since A is symmetric).
180: *
181: VALUE = ZERO
182: K = 1
183: IF( LSAME( UPLO, 'U' ) ) THEN
184: DO 60 J = 1, N
185: SUM = ZERO
186: DO 50 I = 1, J - 1
187: ABSA = ABS( AP( K ) )
188: SUM = SUM + ABSA
189: WORK( I ) = WORK( I ) + ABSA
190: K = K + 1
191: 50 CONTINUE
192: WORK( J ) = SUM + ABS( AP( K ) )
193: K = K + 1
194: 60 CONTINUE
195: DO 70 I = 1, N
196: VALUE = MAX( VALUE, WORK( I ) )
197: 70 CONTINUE
198: ELSE
199: DO 80 I = 1, N
200: WORK( I ) = ZERO
201: 80 CONTINUE
202: DO 100 J = 1, N
203: SUM = WORK( J ) + ABS( AP( K ) )
204: K = K + 1
205: DO 90 I = J + 1, N
206: ABSA = ABS( AP( K ) )
207: SUM = SUM + ABSA
208: WORK( I ) = WORK( I ) + ABSA
209: K = K + 1
210: 90 CONTINUE
211: VALUE = MAX( VALUE, SUM )
212: 100 CONTINUE
213: END IF
214: ELSE IF( ( LSAME( NORM, 'F' ) ) .OR. ( LSAME( NORM, 'E' ) ) ) THEN
215: *
216: * Find normF(A).
217: *
218: SCALE = ZERO
219: SUM = ONE
220: K = 2
221: IF( LSAME( UPLO, 'U' ) ) THEN
222: DO 110 J = 2, N
223: CALL DLASSQ( J-1, AP( K ), 1, SCALE, SUM )
224: K = K + J
225: 110 CONTINUE
226: ELSE
227: DO 120 J = 1, N - 1
228: CALL DLASSQ( N-J, AP( K ), 1, SCALE, SUM )
229: K = K + N - J + 1
230: 120 CONTINUE
231: END IF
232: SUM = 2*SUM
233: K = 1
234: DO 130 I = 1, N
235: IF( AP( K ).NE.ZERO ) THEN
236: ABSA = ABS( AP( K ) )
237: IF( SCALE.LT.ABSA ) THEN
238: SUM = ONE + SUM*( SCALE / ABSA )**2
239: SCALE = ABSA
240: ELSE
241: SUM = SUM + ( ABSA / SCALE )**2
242: END IF
243: END IF
244: IF( LSAME( UPLO, 'U' ) ) THEN
245: K = K + I + 1
246: ELSE
247: K = K + N - I + 1
248: END IF
249: 130 CONTINUE
250: VALUE = SCALE*SQRT( SUM )
251: END IF
252: *
253: DLANSP = VALUE
254: RETURN
255: *
256: * End of DLANSP
257: *
258: END
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