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DOUBLE PRECISION FUNCTION ZLANTB( NORM, UPLO, DIAG, N, K, AB,
$ LDAB, WORK ) * * -- LAPACK auxiliary routine (version 3.2) -- * -- LAPACK is a software package provided by Univ. of Tennessee, -- * -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..-- * November 2006 * * .. Scalar Arguments .. CHARACTER DIAG, NORM, UPLO INTEGER K, LDAB, N * .. * .. Array Arguments .. DOUBLE PRECISION WORK( * ) COMPLEX*16 AB( LDAB, * ) * .. * * Purpose * ======= * * ZLANTB returns the value of the one norm, or the Frobenius norm, or * the infinity norm, or the element of largest absolute value of an * n by n triangular band matrix A, with ( k + 1 ) diagonals. * * Description * =========== * * ZLANTB returns the value * * ZLANTB = ( 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 ZLANTB as described * above. * * UPLO (input) CHARACTER*1 * Specifies whether the matrix A is upper or lower triangular. * = 'U': Upper triangular * = 'L': Lower triangular * * DIAG (input) CHARACTER*1 * Specifies whether or not the matrix A is unit triangular. * = 'N': Non-unit triangular * = 'U': Unit triangular * * N (input) INTEGER * The order of the matrix A. N >= 0. When N = 0, ZLANTB is * set to zero. * * K (input) INTEGER * The number of super-diagonals of the matrix A if UPLO = 'U', * or the number of sub-diagonals of the matrix A if UPLO = 'L'. * K >= 0. * * AB (input) COMPLEX*16 array, dimension (LDAB,N) * The upper or lower triangular band matrix A, stored in the * first k+1 rows of AB. The j-th column of A is stored * in the j-th column of the array AB as follows: * if UPLO = 'U', AB(k+1+i-j,j) = A(i,j) for max(1,j-k)<=i<=j; * if UPLO = 'L', AB(1+i-j,j) = A(i,j) for j<=i<=min(n,j+k). * Note that when DIAG = 'U', the elements of the array AB * corresponding to the diagonal elements of the matrix A are * not referenced, but are assumed to be one. * * LDAB (input) INTEGER * The leading dimension of the array AB. LDAB >= K+1. * * WORK (workspace) DOUBLE PRECISION array, dimension (MAX(1,LWORK)), * where LWORK >= N when NORM = 'I'; otherwise, WORK is not * referenced. * * ===================================================================== * * .. Parameters .. DOUBLE PRECISION ONE, ZERO PARAMETER ( ONE = 1.0D+0, ZERO = 0.0D+0 ) * .. * .. Local Scalars .. LOGICAL UDIAG INTEGER I, J, L DOUBLE PRECISION SCALE, SUM, VALUE * .. * .. External Functions .. LOGICAL LSAME EXTERNAL LSAME * .. * .. External Subroutines .. EXTERNAL ZLASSQ * .. * .. Intrinsic Functions .. INTRINSIC ABS, MAX, MIN, SQRT * .. * .. Executable Statements .. * IF( N.EQ.0 ) THEN VALUE = ZERO ELSE IF( LSAME( NORM, 'M' ) ) THEN * * Find max(abs(A(i,j))). * IF( LSAME( DIAG, 'U' ) ) THEN VALUE = ONE IF( LSAME( UPLO, 'U' ) ) THEN DO 20 J = 1, N DO 10 I = MAX( K+2-J, 1 ), K VALUE = MAX( VALUE, ABS( AB( I, J ) ) ) 10 CONTINUE 20 CONTINUE ELSE DO 40 J = 1, N DO 30 I = 2, MIN( N+1-J, K+1 ) VALUE = MAX( VALUE, ABS( AB( I, J ) ) ) 30 CONTINUE 40 CONTINUE END IF ELSE VALUE = ZERO IF( LSAME( UPLO, 'U' ) ) THEN DO 60 J = 1, N DO 50 I = MAX( K+2-J, 1 ), K + 1 VALUE = MAX( VALUE, ABS( AB( I, J ) ) ) 50 CONTINUE 60 CONTINUE ELSE DO 80 J = 1, N DO 70 I = 1, MIN( N+1-J, K+1 ) VALUE = MAX( VALUE, ABS( AB( I, J ) ) ) 70 CONTINUE 80 CONTINUE END IF END IF ELSE IF( ( LSAME( NORM, 'O' ) ) .OR. ( NORM.EQ.'1' ) ) THEN * * Find norm1(A). * VALUE = ZERO UDIAG = LSAME( DIAG, 'U' ) IF( LSAME( UPLO, 'U' ) ) THEN DO 110 J = 1, N IF( UDIAG ) THEN SUM = ONE DO 90 I = MAX( K+2-J, 1 ), K SUM = SUM + ABS( AB( I, J ) ) 90 CONTINUE ELSE SUM = ZERO DO 100 I = MAX( K+2-J, 1 ), K + 1 SUM = SUM + ABS( AB( I, J ) ) 100 CONTINUE END IF VALUE = MAX( VALUE, SUM ) 110 CONTINUE ELSE DO 140 J = 1, N IF( UDIAG ) THEN SUM = ONE DO 120 I = 2, MIN( N+1-J, K+1 ) SUM = SUM + ABS( AB( I, J ) ) 120 CONTINUE ELSE SUM = ZERO DO 130 I = 1, MIN( N+1-J, K+1 ) SUM = SUM + ABS( AB( I, J ) ) 130 CONTINUE END IF VALUE = MAX( VALUE, SUM ) 140 CONTINUE END IF ELSE IF( LSAME( NORM, 'I' ) ) THEN * * Find normI(A). * VALUE = ZERO IF( LSAME( UPLO, 'U' ) ) THEN IF( LSAME( DIAG, 'U' ) ) THEN DO 150 I = 1, N WORK( I ) = ONE 150 CONTINUE DO 170 J = 1, N L = K + 1 - J DO 160 I = MAX( 1, J-K ), J - 1 WORK( I ) = WORK( I ) + ABS( AB( L+I, J ) ) 160 CONTINUE 170 CONTINUE ELSE DO 180 I = 1, N WORK( I ) = ZERO 180 CONTINUE DO 200 J = 1, N L = K + 1 - J DO 190 I = MAX( 1, J-K ), J WORK( I ) = WORK( I ) + ABS( AB( L+I, J ) ) 190 CONTINUE 200 CONTINUE END IF ELSE IF( LSAME( DIAG, 'U' ) ) THEN DO 210 I = 1, N WORK( I ) = ONE 210 CONTINUE DO 230 J = 1, N L = 1 - J DO 220 I = J + 1, MIN( N, J+K ) WORK( I ) = WORK( I ) + ABS( AB( L+I, J ) ) 220 CONTINUE 230 CONTINUE ELSE DO 240 I = 1, N WORK( I ) = ZERO 240 CONTINUE DO 260 J = 1, N L = 1 - J DO 250 I = J, MIN( N, J+K ) WORK( I ) = WORK( I ) + ABS( AB( L+I, J ) ) 250 CONTINUE 260 CONTINUE END IF END IF DO 270 I = 1, N VALUE = MAX( VALUE, WORK( I ) ) 270 CONTINUE ELSE IF( ( LSAME( NORM, 'F' ) ) .OR. ( LSAME( NORM, 'E' ) ) ) THEN * * Find normF(A). * IF( LSAME( UPLO, 'U' ) ) THEN IF( LSAME( DIAG, 'U' ) ) THEN SCALE = ONE SUM = N IF( K.GT.0 ) THEN DO 280 J = 2, N CALL ZLASSQ( MIN( J-1, K ), $ AB( MAX( K+2-J, 1 ), J ), 1, SCALE, $ SUM ) 280 CONTINUE END IF ELSE SCALE = ZERO SUM = ONE DO 290 J = 1, N CALL ZLASSQ( MIN( J, K+1 ), AB( MAX( K+2-J, 1 ), J ), $ 1, SCALE, SUM ) 290 CONTINUE END IF ELSE IF( LSAME( DIAG, 'U' ) ) THEN SCALE = ONE SUM = N IF( K.GT.0 ) THEN DO 300 J = 1, N - 1 CALL ZLASSQ( MIN( N-J, K ), AB( 2, J ), 1, SCALE, $ SUM ) 300 CONTINUE END IF ELSE SCALE = ZERO SUM = ONE DO 310 J = 1, N CALL ZLASSQ( MIN( N-J+1, K+1 ), AB( 1, J ), 1, SCALE, $ SUM ) 310 CONTINUE END IF END IF VALUE = SCALE*SQRT( SUM ) END IF * ZLANTB = VALUE RETURN * * End of ZLANTB * END |