`isbanded`

Tests whether a matrix lies within a given band.

Category: Mathematics > Linear Algebra

Syntax

tf = isbanded(A, lower, upper)

True if A has all its nonzeros within lower diagonals below and upper diagonals above the main diagonal.

Description

isbanded(A,0,0) tests for a diagonal matrix, isbanded(A,1,1) for a tridiagonal one, isbanded(A,n-1,0) for lower triangular. The matrix may have narrower bandwidth than asked: a diagonal matrix is banded for any lower and upper.

Input arguments

A: Numeric matrix.
lower, upper: Non-negative integers giving the lower and upper bandwidth to test.

Output arguments

tf: Logical scalar.

Example

Tridiagonal test

A = [1 2 0; 3 4 5; 0 6 7];
isbanded(A, 1, 1)
isbanded(A, 0, 1)

Output

ans = logical
   1
ans = logical
   0

See also

bandwidth isdiag istril istriu