Developer Reference for Intel® oneAPI Math Kernel Library for Fortran

ID 766686
Date 3/22/2024
Public

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?langt

Returns the value of the 1-norm, Frobenius norm, infinity-norm, or the largest absolute value of any element of a general tridiagonal matrix.

Syntax

val = slangt( norm, n, dl, d, du )

val = dlangt( norm, n, dl, d, du )

val = clangt( norm, n, dl, d, du )

val = zlangt( norm, n, dl, d, du )

Include Files

  • mkl.fi

Description

The routine returns the value of the 1-norm, or the Frobenius norm, or the infinity norm, or the element of largest absolute value of a real/complex tridiagonal matrix A.

Input Parameters

norm

CHARACTER*1. Specifies the value to be returned by the routine:

= 'M' or 'm': val = max(abs(Aij)), largest absolute value of the matrix A.

= '1' or 'O' or 'o': val = norm1(A), 1-norm of the matrix A (maximum column sum),

= 'I' or 'i': val = normI(A), infinity norm of the matrix A (maximum row sum),

= 'F', 'f', 'E' or 'e': val = normF(A), Frobenius norm of the matrix A (square root of sum of squares).

n

INTEGER. The order of the matrix A. n 0. When n = 0, ?langt is set to zero.

dl, d, du

REAL for slangt

DOUBLE PRECISION for dlangt

COMPLEX for clangt

DOUBLE COMPLEX for zlangt

Arrays: dl (n-1), d (n), du (n-1).

The array dl contains the (n-1) sub-diagonal elements of A.

The array d contains the diagonal elements of A.

The array du contains the (n-1) super-diagonal elements of A.

Output Parameters

val

REAL for slangt/clangt

DOUBLE PRECISION for dlangt/zlangt

Value returned by the function.