MATLAB: How to plot the l2 norm circle

circlenorm

Hi all,
I'm trying to visualize the l2 norm circle. It seems easy but I'm stuck. This is the code I write to plot the circle (based on x^2 + y^2 = 1):
clear; clc;
x = -1:0.01:1;
y = sqrt(1 - x .^ 2);
plot(x, y)
hold on
plot(y, x)
axis square
It gives me a figure like this:
apparently the left lower part is missing, what I do not understand is that both x and y are non-negative, why would l2 norm gives a full circle where left lower part is negative for both x and y?
Please forgive me if I did not explain mathematically enough.

Best Answer

theta=0:2*pi/100:2*pi;
x=cos(theta);
y=sin(theta);
plot(x,y)
Best wishes
Torsten.
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