How do I plot the infinite norm of a matrix on a graph?. I should have a square but I end up having a circle

A=[2 0;1 -1]; Matrix A %(Sample Matrix)

infnorm=norm(A,inf) %Infinite norm

theta=linspace(0,2*pi,601); % Using 601 points

x=[cos(theta);sin(theta)];

plot(infnorm*x(1,:),infnorm*x(2,:),'--'), axis equal

title('Unit circle in Infinite-norm')

xlabel('x_1'), ylabel('x_2') %labels

Answer 1

[Sam Chak]

Hi @Muhideen Ogunlowo

Perhaps you want to plot something like this:

p = [1, 2^1, 2^2, 2^3, 2^4];

for j = 1:length(p)
    f = @(x,y) abs(x).^p(j) + abs(y).^p(j) - 1;
    fimplicit(f, [-3/2, 3/2, -3/2, 3/2])
    hold on
end

hold off
grid on, xlabel('x_{1}'), ylabel('x_{2}')
axis square
title({'Unit circles in the $p$-norm'}, 'interpreter', 'latex', 'FontSize', 12)
text(0.25, 0.4, 'p = 1', 'FontSize', 9)
text(0.60, 0.60, '2',    'FontSize', 9)
text(0.75, 0.77, '4',    'FontSize', 9)
text(0.85, 0.88, '8',    'FontSize', 9)
text(1.00, 1.04, '16',   'FontSize', 9)

[Muhideen Ogunlowo]

Something like that, but I am looking for the graph of the infinite norm of the matrix I have. A more prefarable solution to my problem would be a code that graphs the infinite norm of any matrix

[Sam Chak]

Hi @Muhideen Ogunlowo,

The infinity norm of a matrix returns a scalar value. Could you please describe exactly how you would like to plot the square?

[Muhideen Ogunlowo]

I think the code is fine, I just didn't understand it at first

[Sam Chak]

Hi @Muhideen Ogunlowo

Has your problem been solved? If so, could you please run the code and share the square plot here?