# 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 onplot(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.

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