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NAME DLANGT - return the value of the one norm, or the Frobenius norm, or the infinity norm, or the element of largest abso- lute value of a real tridiagonal matrix A SYNOPSIS DOUBLE PRECISION FUNCTION DLANGT( NORM, N, DL, D, DU ) CHARACTER NORM INTEGER N DOUBLE PRECISION D( * ), DL( * ), DU( * ) 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. DESCRIPTION DLANGT returns the value DLANGT = ( 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 matrix norm. ARGUMENTS NORM (input) CHARACTER*1 Specifies the value to be returned in DLANGT as described above. N (input) INTEGER The order of the matrix A. N >= 0. When N = 0, DLANGT is set to zero. DL (input) DOUBLE PRECISION array, dimension (N-1) The (n-1) sub-diagonal elements of A. D (input) DOUBLE PRECISION array, dimension (N) The diagonal elements of A. DU (input) DOUBLE PRECISION array, dimension (N-1) The (n-1) super-diagonal elements of A.