NR1RB

Computes the 1-norm of a real band matrix in band storage mode.

Required Arguments

A — Real (NUCA + NLCA + 1) by N array containing the N by N band matrix in band storage mode. (Input)

NLCA — Number of lower codiagonals of A. (Input)

NUCA — Number of upper codiagonals of A. (Input)

ANORM — Real scalar containing the 1-norm of A. (Output)

N — Order of the matrix. (Input)
Default: N = SIZE (A,2).

LDA — Leading dimension of A exactly as specified in the dimension statement of the calling program. (Input)
Default: LDA = SIZE (A,1).

Generic: CALL NR1RB (A, NLCA, NUCA, ANORM [, …])

Specific: The specific interface names are S_NR1RB and D_NR1RB.

Single: CALL NR1RB (N, A, LDA, NLCA, NUCA, ANORM)

Double: The double precision name is DNR1RB.

The routine NR1RB computes the 1-norm of a real band matrix A. The 1-norm of a matrix A is

This is the maximum of the sums of the absolute values of the column elements.

Compute the 1-norm of a 4 × 4 real band matrix stored in band mode.

USE NR1RB_INT

USE UMACH_INT

IMPLICIT NONE

! Declare variables

INTEGER LDA, N, NLCA, NUCA

PARAMETER (LDA=4, N=4, NLCA=2, NUCA=1)

INTEGER NOUT

REAL A(LDA,N), ANORM

! Set values for A (in band mode)

! A = ( 0.0 2.0 2.0 3.0 )

! ( -2.0 -3.0 -4.0 -1.0 )

! ( 2.0 1.0 0.0 0.0 )

! ( 0.0 1.0 0.0 0.0 )

DATA A/0.0, -2.0, 2.0, 0.0, 2.0, -3.0, 1.0, 1.0, 2.0, -4.0, 0.0, &

0.0, 3.0, -1.0, 2*0.0/

! Compute the L1 norm of A

CALL NR1RB (A, NLCA, NUCA, ANORM)

! Print results

CALL UMACH (2, NOUT)

WRITE (NOUT,*) ' The 1-norm of A is ', ANORM

END

Output

The 1-norm of A is 7.00000