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DOUBLE PRECISION FUNCTION DLANSP( NORM, UPLO, N, AP, WORK )
*
* -- LAPACK auxiliary routine (version 3.1) --
* Univ. of Tennessee, Univ. of California Berkeley and NAG Ltd..
* November 2006
*
* .. Scalar Arguments ..
CHARACTER NORM, UPLO
INTEGER N
* ..
* .. Array Arguments ..
DOUBLE PRECISION AP( * ), WORK( * )
* ..
*
* Purpose
* =======
*
* DLANSP returns the value of the one norm, or the Frobenius norm, or
* the infinity norm, or the element of largest absolute value of a
* real symmetric matrix A, supplied in packed form.
*
* Description
* ===========
*
* DLANSP returns the value
*
* DLANSP = ( max(abs(A(i,j))), NORM = 'M' or 'm'
* (
* ( norm1(A), NORM = '1', 'O' or 'o'
* (
* ( normI(A), NORM = 'I' or 'i'
* (
* ( normF(A), NORM = 'F', 'f', 'E' or 'e'
*
* where norm1 denotes the one norm of a matrix (maximum column sum),
* normI denotes the infinity norm of a matrix (maximum row sum) and
* normF denotes the Frobenius norm of a matrix (square root of sum of
* squares). Note that max(abs(A(i,j))) is not a consistent matrix norm.
*
* Arguments
* =========
*
* NORM (input) CHARACTER*1
* Specifies the value to be returned in DLANSP as described
* above.
*
* UPLO (input) CHARACTER*1
* Specifies whether the upper or lower triangular part of the
* symmetric matrix A is supplied.
* = 'U': Upper triangular part of A is supplied
* = 'L': Lower triangular part of A is supplied
*
* N (input) INTEGER
* The order of the matrix A. N >= 0. When N = 0, DLANSP is
* set to zero.
*
* AP (input) DOUBLE PRECISION array, dimension (N*(N+1)/2)
* The upper or lower triangle of the symmetric matrix A, packed
* columnwise in a linear array. The j-th column of A is stored
* in the array AP as follows:
* if UPLO = 'U', AP(i + (j-1)*j/2) = A(i,j) for 1<=i<=j;
* if UPLO = 'L', AP(i + (j-1)*(2n-j)/2) = A(i,j) for j<=i<=n.
*
* WORK (workspace) DOUBLE PRECISION array, dimension (MAX(1,LWORK)),
* where LWORK >= N when NORM = 'I' or '1' or 'O'; otherwise,
* WORK is not referenced.
*
* =====================================================================
*
* .. Parameters ..
DOUBLE PRECISION ONE, ZERO
PARAMETER ( ONE = 1.0D+0, ZERO = 0.0D+0 )
* ..
* .. Local Scalars ..
INTEGER I, J, K
DOUBLE PRECISION ABSA, SCALE, SUM, VALUE
* ..
* .. External Subroutines ..
EXTERNAL DLASSQ
* ..
* .. External Functions ..
LOGICAL LSAME
EXTERNAL LSAME
* ..
* .. Intrinsic Functions ..
INTRINSIC ABS, MAX, SQRT
* ..
* .. Executable Statements ..
*
IF( N.EQ.0 ) THEN
VALUE = ZERO
ELSE IF( LSAME( NORM, 'M' ) ) THEN
*
* Find max(abs(A(i,j))).
*
VALUE = ZERO
IF( LSAME( UPLO, 'U' ) ) THEN
K = 1
DO 20 J = 1, N
DO 10 I = K, K + J - 1
VALUE = MAX( VALUE, ABS( AP( I ) ) )
10 CONTINUE
K = K + J
20 CONTINUE
ELSE
K = 1
DO 40 J = 1, N
DO 30 I = K, K + N - J
VALUE = MAX( VALUE, ABS( AP( I ) ) )
30 CONTINUE
K = K + N - J + 1
40 CONTINUE
END IF
ELSE IF( ( LSAME( NORM, 'I' ) ) .OR. ( LSAME( NORM, 'O' ) ) .OR.
$ ( NORM.EQ.'1' ) ) THEN
*
* Find normI(A) ( = norm1(A), since A is symmetric).
*
VALUE = ZERO
K = 1
IF( LSAME( UPLO, 'U' ) ) THEN
DO 60 J = 1, N
SUM = ZERO
DO 50 I = 1, J - 1
ABSA = ABS( AP( K ) )
SUM = SUM + ABSA
WORK( I ) = WORK( I ) + ABSA
K = K + 1
50 CONTINUE
WORK( J ) = SUM + ABS( AP( K ) )
K = K + 1
60 CONTINUE
DO 70 I = 1, N
VALUE = MAX( VALUE, WORK( I ) )
70 CONTINUE
ELSE
DO 80 I = 1, N
WORK( I ) = ZERO
80 CONTINUE
DO 100 J = 1, N
SUM = WORK( J ) + ABS( AP( K ) )
K = K + 1
DO 90 I = J + 1, N
ABSA = ABS( AP( K ) )
SUM = SUM + ABSA
WORK( I ) = WORK( I ) + ABSA
K = K + 1
90 CONTINUE
VALUE = MAX( VALUE, SUM )
100 CONTINUE
END IF
ELSE IF( ( LSAME( NORM, 'F' ) ) .OR. ( LSAME( NORM, 'E' ) ) ) THEN
*
* Find normF(A).
*
SCALE = ZERO
SUM = ONE
K = 2
IF( LSAME( UPLO, 'U' ) ) THEN
DO 110 J = 2, N
CALL DLASSQ( J-1, AP( K ), 1, SCALE, SUM )
K = K + J
110 CONTINUE
ELSE
DO 120 J = 1, N - 1
CALL DLASSQ( N-J, AP( K ), 1, SCALE, SUM )
K = K + N - J + 1
120 CONTINUE
END IF
SUM = 2*SUM
K = 1
DO 130 I = 1, N
IF( AP( K ).NE.ZERO ) THEN
ABSA = ABS( AP( K ) )
IF( SCALE.LT.ABSA ) THEN
SUM = ONE + SUM*( SCALE / ABSA )**2
SCALE = ABSA
ELSE
SUM = SUM + ( ABSA / SCALE )**2
END IF
END IF
IF( LSAME( UPLO, 'U' ) ) THEN
K = K + I + 1
ELSE
K = K + N - I + 1
END IF
130 CONTINUE
VALUE = SCALE*SQRT( SUM )
END IF
*
DLANSP = VALUE
RETURN
*
* End of DLANSP
*
END
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