.TH DLANGT 1 "November 2006" " LAPACK auxiliary routine (version 3.1) " " LAPACK auxiliary routine (version 3.1) " .SH NAME DLANGT - the value of the one norm, or the Frobenius norm, or the infinity norm, or the element of largest absolute value of a real tridiagonal matrix A .SH SYNOPSIS .TP 17 DOUBLE PRECISION FUNCTION DLANGT( NORM, N, DL, D, DU ) .TP 17 .ti +4 CHARACTER NORM .TP 17 .ti +4 INTEGER N .TP 17 .ti +4 DOUBLE PRECISION D( * ), DL( * ), DU( * ) .SH PURPOSE DLANGT 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 tridiagonal matrix A. .SH DESCRIPTION DLANGT returns the value .br DLANGT = ( max(abs(A(i,j))), NORM = \(aqM\(aq or \(aqm\(aq .br ( .br ( norm1(A), NORM = \(aq1\(aq, \(aqO\(aq or \(aqo\(aq .br ( .br ( normI(A), NORM = \(aqI\(aq or \(aqi\(aq .br ( .br ( normF(A), NORM = \(aqF\(aq, \(aqf\(aq, \(aqE\(aq or \(aqe\(aq 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. .SH ARGUMENTS .TP 8 NORM (input) CHARACTER*1 Specifies the value to be returned in DLANGT as described above. .TP 8 N (input) INTEGER The order of the matrix A. N >= 0. When N = 0, DLANGT is set to zero. .TP 8 DL (input) DOUBLE PRECISION array, dimension (N-1) The (n-1) sub-diagonal elements of A. .TP 8 D (input) DOUBLE PRECISION array, dimension (N) The diagonal elements of A. .TP 8 DU (input) DOUBLE PRECISION array, dimension (N-1) The (n-1) super-diagonal elements of A.