Annotation of rpl/lapack/lapack/zlangt.f, revision 1.1
1.1 ! bertrand 1: DOUBLE PRECISION FUNCTION ZLANGT( NORM, N, DL, D, DU )
! 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
! 10: INTEGER N
! 11: * ..
! 12: * .. Array Arguments ..
! 13: COMPLEX*16 D( * ), DL( * ), DU( * )
! 14: * ..
! 15: *
! 16: * Purpose
! 17: * =======
! 18: *
! 19: * ZLANGT returns the value of the one norm, or the Frobenius norm, or
! 20: * the infinity norm, or the element of largest absolute value of a
! 21: * complex tridiagonal matrix A.
! 22: *
! 23: * Description
! 24: * ===========
! 25: *
! 26: * ZLANGT returns the value
! 27: *
! 28: * ZLANGT = ( max(abs(A(i,j))), NORM = 'M' or 'm'
! 29: * (
! 30: * ( norm1(A), NORM = '1', 'O' or 'o'
! 31: * (
! 32: * ( normI(A), NORM = 'I' or 'i'
! 33: * (
! 34: * ( normF(A), NORM = 'F', 'f', 'E' or 'e'
! 35: *
! 36: * where norm1 denotes the one norm of a matrix (maximum column sum),
! 37: * normI denotes the infinity norm of a matrix (maximum row sum) and
! 38: * normF denotes the Frobenius norm of a matrix (square root of sum of
! 39: * squares). Note that max(abs(A(i,j))) is not a consistent matrix norm.
! 40: *
! 41: * Arguments
! 42: * =========
! 43: *
! 44: * NORM (input) CHARACTER*1
! 45: * Specifies the value to be returned in ZLANGT as described
! 46: * above.
! 47: *
! 48: * N (input) INTEGER
! 49: * The order of the matrix A. N >= 0. When N = 0, ZLANGT is
! 50: * set to zero.
! 51: *
! 52: * DL (input) COMPLEX*16 array, dimension (N-1)
! 53: * The (n-1) sub-diagonal elements of A.
! 54: *
! 55: * D (input) COMPLEX*16 array, dimension (N)
! 56: * The diagonal elements of A.
! 57: *
! 58: * DU (input) COMPLEX*16 array, dimension (N-1)
! 59: * The (n-1) super-diagonal elements of A.
! 60: *
! 61: * =====================================================================
! 62: *
! 63: * .. Parameters ..
! 64: DOUBLE PRECISION ONE, ZERO
! 65: PARAMETER ( ONE = 1.0D+0, ZERO = 0.0D+0 )
! 66: * ..
! 67: * .. Local Scalars ..
! 68: INTEGER I
! 69: DOUBLE PRECISION ANORM, SCALE, SUM
! 70: * ..
! 71: * .. External Functions ..
! 72: LOGICAL LSAME
! 73: EXTERNAL LSAME
! 74: * ..
! 75: * .. External Subroutines ..
! 76: EXTERNAL ZLASSQ
! 77: * ..
! 78: * .. Intrinsic Functions ..
! 79: INTRINSIC ABS, MAX, SQRT
! 80: * ..
! 81: * .. Executable Statements ..
! 82: *
! 83: IF( N.LE.0 ) THEN
! 84: ANORM = ZERO
! 85: ELSE IF( LSAME( NORM, 'M' ) ) THEN
! 86: *
! 87: * Find max(abs(A(i,j))).
! 88: *
! 89: ANORM = ABS( D( N ) )
! 90: DO 10 I = 1, N - 1
! 91: ANORM = MAX( ANORM, ABS( DL( I ) ) )
! 92: ANORM = MAX( ANORM, ABS( D( I ) ) )
! 93: ANORM = MAX( ANORM, ABS( DU( I ) ) )
! 94: 10 CONTINUE
! 95: ELSE IF( LSAME( NORM, 'O' ) .OR. NORM.EQ.'1' ) THEN
! 96: *
! 97: * Find norm1(A).
! 98: *
! 99: IF( N.EQ.1 ) THEN
! 100: ANORM = ABS( D( 1 ) )
! 101: ELSE
! 102: ANORM = MAX( ABS( D( 1 ) )+ABS( DL( 1 ) ),
! 103: $ ABS( D( N ) )+ABS( DU( N-1 ) ) )
! 104: DO 20 I = 2, N - 1
! 105: ANORM = MAX( ANORM, ABS( D( I ) )+ABS( DL( I ) )+
! 106: $ ABS( DU( I-1 ) ) )
! 107: 20 CONTINUE
! 108: END IF
! 109: ELSE IF( LSAME( NORM, 'I' ) ) THEN
! 110: *
! 111: * Find normI(A).
! 112: *
! 113: IF( N.EQ.1 ) THEN
! 114: ANORM = ABS( D( 1 ) )
! 115: ELSE
! 116: ANORM = MAX( ABS( D( 1 ) )+ABS( DU( 1 ) ),
! 117: $ ABS( D( N ) )+ABS( DL( N-1 ) ) )
! 118: DO 30 I = 2, N - 1
! 119: ANORM = MAX( ANORM, ABS( D( I ) )+ABS( DU( I ) )+
! 120: $ ABS( DL( I-1 ) ) )
! 121: 30 CONTINUE
! 122: END IF
! 123: ELSE IF( ( LSAME( NORM, 'F' ) ) .OR. ( LSAME( NORM, 'E' ) ) ) THEN
! 124: *
! 125: * Find normF(A).
! 126: *
! 127: SCALE = ZERO
! 128: SUM = ONE
! 129: CALL ZLASSQ( N, D, 1, SCALE, SUM )
! 130: IF( N.GT.1 ) THEN
! 131: CALL ZLASSQ( N-1, DL, 1, SCALE, SUM )
! 132: CALL ZLASSQ( N-1, DU, 1, SCALE, SUM )
! 133: END IF
! 134: ANORM = SCALE*SQRT( SUM )
! 135: END IF
! 136: *
! 137: ZLANGT = ANORM
! 138: RETURN
! 139: *
! 140: * End of ZLANGT
! 141: *
! 142: END
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