MATLAB legend does not work for plotting 2 circles - matlab

Question

close all; clc; clear all;
A0 = 1.5; % meters
lambda = 100 % meters
k = (2*pi)/lambda;
T = 3600 % Period in seconds
ome = 2*pi/T; % omega
x = 0; z = 0;
t = linspace(0,7200,100); % 2 periods, 100 data
zz=0;
for z = 0:20:20;
zz = zz+1;
% multiplied by 100, unit in cm/s
u= 100.*ome*A0*exp(-k*z)*sin(k*x - ome*t);
w = 100.*-ome*A0*exp(-k*z)*cos(k*x - ome*t);
uu(zz,:) = u; % size(uu) 2 100
ww(zz,:) = w; % size(ww) 2 100
end
figure(1)
color = -0.8;
for zz = 1:2
color = color + 0.8;
for i=1:3:49; % plot circle for one period
plot([uu(zz,i) uu(zz,i+3)],[ww(zz,i) ww(zz,i+3)], 'color',([color+0.2 0 0]), 'linewidth', 2)
hold on
end
end
title('Plot of lines from (0,0) to (u(i), v(i). Radius or amplitude in cm/s')
axis equal;
grid on;
legend('radius at surface','radius at depth 20')%
This script plots 2 circles: the small one is red, another is black. But the legend is not consistence with these circles.

Answer 1

this is because you create many line objects in your axes (each loop iteration when you do plot) and the legend function addresses these line objects. sp line1 and line2 are still part of the polygon you draw.
I'll answer your question, but know that your code is sub-optimal and that it is not the best way to draw 2 circles or polygons.
so with minimal change to your code this is what you can do:
....
figure(1)
color = -0.8;
for zz = 1:2
color = color + 0.8;
for i=1:3:49; % plot circle for one period
h(zz)=plot([uu(zz,i) uu(zz,i+3)],[ww(zz,i) ww(zz,i+3)], 'color',([color+0.2 0 0]), 'linewidth', 2)
hold on
end
end
title('Plot of lines from (0,0) to (u(i), v(i). Radius or amplitude in cm/s')
axis equal;
grid on;
legend([h(1) h(2)],{'radius at surface','radius at depth 20'});