conditional colouring graph problem
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Hey, I have a problem with changing the colours on my graph conditionally; my function is as follows
function [t,vx,vy] = Q3_1400000(rocket,brake)
[t,ax,ay] = getAcceleration(rocket,brake);
vx = 0; vy = 0;
for n = 1:999;
vx(n+1) = vx(n) + ax(n+1);
vy(n+1) = vy(n) + ay(n+1);
k = 1:length(vx);
if vy(k) > vx(k)
c = 'r';
else
c = 'b';
end
end
plot(t,vx(k),c);
hold on
grid on
plot(t,vy(k),c);
xlabel('Time (s)');
ylabel('Velocity (m/s)');
title('\Velocity data for the rocket sled');
legend({'v_x','v_y'})
end
For some reason when the graph plots, the colour will always be the ' else ' colour and won't change at all. Does anybody know the solution to this please ?
Thanks
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Accepted Answer
Chad Greene
on 27 Jan 2015
It looks like you're only testing the condition of whether the very last value in vy is bigger than the very last value in vx because each time it goes through the loop it's overwriting c.
3 Comments
Chad Greene
on 27 Jan 2015
Edited: Chad Greene
on 27 Jan 2015
It's hard to understand exactly what you're trying to do. Perhaps the example below will help. It puts a red circle around all the black y1 points that are bigger than their corresponding blue y2 points:
x = 1:10;
y1 = rand(size(x));
y2 = rand(size(x));
plot(x,y1,'kx',x,y2,'b+')
hold on
% indices of y1 values that are bigger than y2:
ind = y1>y2;
plot(x(ind),y1(ind),'ro')
box off
More Answers (2)
Chad Greene
on 27 Jan 2015
First create a logical array the size of vx and vy. It will have a 1 everywhere vy is bigger than vx, and a zero everywhere else:
vybigger = vy>vx;
Plot vx and vy, both in red where vy is bigger than vx:
plot(t(vybigger),vy(vybigger),'r');
hold on
plot(t(vybigger),vx(vybigger),'r');
Plot the rest of the data in blue:
plot(t(~vybigger),vy(~vybigger),'b');
plot(t(~vybigger),vx(~vybigger),'b');
Kelly Kearney
on 28 Jan 2015
An alternative method to Chad's (which works nicely if there's only one color switch, but may need some modification if there are multiple switches and you want solid lines) is to use patches with interpolated edge color:
t = linspace(0,2*pi,100);
vx = cos(t);
vy = sin(t);
vybigger = vy > vx;
hold on;
h(1) = patch([t NaN], [vx NaN], [vybigger NaN]);
h(2) = patch([t NaN], [vy NaN], [vybigger NaN]);
set(h, 'edgecolor', 'interp');
colormap([0 0 1; 1 0 0]);
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