Annotation of rpl/lapack/lapack/zlanhe.f, revision 1.6
1.1 bertrand 1: DOUBLE PRECISION FUNCTION ZLANHE( NORM, UPLO, N, A, LDA, WORK )
2: *
3: * -- LAPACK auxiliary routine (version 3.2) --
4: * -- LAPACK is a software package provided by Univ. of Tennessee, --
5: * -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
6: * November 2006
7: *
8: * .. Scalar Arguments ..
9: CHARACTER NORM, UPLO
10: INTEGER LDA, N
11: * ..
12: * .. Array Arguments ..
13: DOUBLE PRECISION WORK( * )
14: COMPLEX*16 A( LDA, * )
15: * ..
16: *
17: * Purpose
18: * =======
19: *
20: * ZLANHE returns the value of the one norm, or the Frobenius norm, or
21: * the infinity norm, or the element of largest absolute value of a
22: * complex hermitian matrix A.
23: *
24: * Description
25: * ===========
26: *
27: * ZLANHE returns the value
28: *
29: * ZLANHE = ( max(abs(A(i,j))), NORM = 'M' or 'm'
30: * (
31: * ( norm1(A), NORM = '1', 'O' or 'o'
32: * (
33: * ( normI(A), NORM = 'I' or 'i'
34: * (
35: * ( normF(A), NORM = 'F', 'f', 'E' or 'e'
36: *
37: * where norm1 denotes the one norm of a matrix (maximum column sum),
38: * normI denotes the infinity norm of a matrix (maximum row sum) and
39: * normF denotes the Frobenius norm of a matrix (square root of sum of
40: * squares). Note that max(abs(A(i,j))) is not a consistent matrix norm.
41: *
42: * Arguments
43: * =========
44: *
45: * NORM (input) CHARACTER*1
46: * Specifies the value to be returned in ZLANHE as described
47: * above.
48: *
49: * UPLO (input) CHARACTER*1
50: * Specifies whether the upper or lower triangular part of the
51: * hermitian matrix A is to be referenced.
52: * = 'U': Upper triangular part of A is referenced
53: * = 'L': Lower triangular part of A is referenced
54: *
55: * N (input) INTEGER
56: * The order of the matrix A. N >= 0. When N = 0, ZLANHE is
57: * set to zero.
58: *
59: * A (input) COMPLEX*16 array, dimension (LDA,N)
60: * The hermitian matrix A. If UPLO = 'U', the leading n by n
61: * upper triangular part of A contains the upper triangular part
62: * of the matrix A, and the strictly lower triangular part of A
63: * is not referenced. If UPLO = 'L', the leading n by n lower
64: * triangular part of A contains the lower triangular part of
65: * the matrix A, and the strictly upper triangular part of A is
66: * not referenced. Note that the imaginary parts of the diagonal
67: * elements need not be set and are assumed to be zero.
68: *
69: * LDA (input) INTEGER
70: * The leading dimension of the array A. LDA >= max(N,1).
71: *
72: * WORK (workspace) DOUBLE PRECISION array, dimension (MAX(1,LWORK)),
73: * where LWORK >= N when NORM = 'I' or '1' or 'O'; otherwise,
74: * WORK is not referenced.
75: *
76: * =====================================================================
77: *
78: * .. Parameters ..
79: DOUBLE PRECISION ONE, ZERO
80: PARAMETER ( ONE = 1.0D+0, ZERO = 0.0D+0 )
81: * ..
82: * .. Local Scalars ..
83: INTEGER I, J
84: DOUBLE PRECISION ABSA, SCALE, SUM, VALUE
85: * ..
86: * .. External Functions ..
87: LOGICAL LSAME
88: EXTERNAL LSAME
89: * ..
90: * .. External Subroutines ..
91: EXTERNAL ZLASSQ
92: * ..
93: * .. Intrinsic Functions ..
94: INTRINSIC ABS, DBLE, MAX, SQRT
95: * ..
96: * .. Executable Statements ..
97: *
98: IF( N.EQ.0 ) THEN
99: VALUE = ZERO
100: ELSE IF( LSAME( NORM, 'M' ) ) THEN
101: *
102: * Find max(abs(A(i,j))).
103: *
104: VALUE = ZERO
105: IF( LSAME( UPLO, 'U' ) ) THEN
106: DO 20 J = 1, N
107: DO 10 I = 1, J - 1
108: VALUE = MAX( VALUE, ABS( A( I, J ) ) )
109: 10 CONTINUE
110: VALUE = MAX( VALUE, ABS( DBLE( A( J, J ) ) ) )
111: 20 CONTINUE
112: ELSE
113: DO 40 J = 1, N
114: VALUE = MAX( VALUE, ABS( DBLE( A( J, J ) ) ) )
115: DO 30 I = J + 1, N
116: VALUE = MAX( VALUE, ABS( A( I, J ) ) )
117: 30 CONTINUE
118: 40 CONTINUE
119: END IF
120: ELSE IF( ( LSAME( NORM, 'I' ) ) .OR. ( LSAME( NORM, 'O' ) ) .OR.
121: $ ( NORM.EQ.'1' ) ) THEN
122: *
123: * Find normI(A) ( = norm1(A), since A is hermitian).
124: *
125: VALUE = ZERO
126: IF( LSAME( UPLO, 'U' ) ) THEN
127: DO 60 J = 1, N
128: SUM = ZERO
129: DO 50 I = 1, J - 1
130: ABSA = ABS( A( I, J ) )
131: SUM = SUM + ABSA
132: WORK( I ) = WORK( I ) + ABSA
133: 50 CONTINUE
134: WORK( J ) = SUM + ABS( DBLE( A( J, J ) ) )
135: 60 CONTINUE
136: DO 70 I = 1, N
137: VALUE = MAX( VALUE, WORK( I ) )
138: 70 CONTINUE
139: ELSE
140: DO 80 I = 1, N
141: WORK( I ) = ZERO
142: 80 CONTINUE
143: DO 100 J = 1, N
144: SUM = WORK( J ) + ABS( DBLE( A( J, J ) ) )
145: DO 90 I = J + 1, N
146: ABSA = ABS( A( I, J ) )
147: SUM = SUM + ABSA
148: WORK( I ) = WORK( I ) + ABSA
149: 90 CONTINUE
150: VALUE = MAX( VALUE, SUM )
151: 100 CONTINUE
152: END IF
153: ELSE IF( ( LSAME( NORM, 'F' ) ) .OR. ( LSAME( NORM, 'E' ) ) ) THEN
154: *
155: * Find normF(A).
156: *
157: SCALE = ZERO
158: SUM = ONE
159: IF( LSAME( UPLO, 'U' ) ) THEN
160: DO 110 J = 2, N
161: CALL ZLASSQ( J-1, A( 1, J ), 1, SCALE, SUM )
162: 110 CONTINUE
163: ELSE
164: DO 120 J = 1, N - 1
165: CALL ZLASSQ( N-J, A( J+1, J ), 1, SCALE, SUM )
166: 120 CONTINUE
167: END IF
168: SUM = 2*SUM
169: DO 130 I = 1, N
170: IF( DBLE( A( I, I ) ).NE.ZERO ) THEN
171: ABSA = ABS( DBLE( A( I, I ) ) )
172: IF( SCALE.LT.ABSA ) THEN
173: SUM = ONE + SUM*( SCALE / ABSA )**2
174: SCALE = ABSA
175: ELSE
176: SUM = SUM + ( ABSA / SCALE )**2
177: END IF
178: END IF
179: 130 CONTINUE
180: VALUE = SCALE*SQRT( SUM )
181: END IF
182: *
183: ZLANHE = VALUE
184: RETURN
185: *
186: * End of ZLANHE
187: *
188: END
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