# Assigning Specific Color Values when MATLAB plots several data sets simultaneously.

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Michael McDermott on 13 May 2020
Commented: Michael McDermott on 13 May 2020
I am having trouble trying to figure out how to change the color of my plots when I am plotting a 2D array of y-values, along with t-values....
The context of the problem is this: I am plotting PREDATOR vs. PREY relations in nature, and thus at each time value t, there are two y-values, one for the predators, and one for the prey. In previous plots, I could change the color of each line to a particular RGB calue (making very beautiful plots), but only because the plot function was fun once for each plot created. (and then the 'hold on;' function was used).... This time however, the two sets are plotted at the same time, so using ->
plot(t,y,'color',k');
will result in "both" plots becoming black. Otherwise, the default colors are used. I am sure there is a way to change this. Any suggestions? I have included my code below. The functions use a 2nd-order Runge Kutta Approximation for ODE's and two differential equations if that helps... Thank you in advance!
%% MAIN SCRIPT - Numerical Method; System of Linear 1rst Order ODE's.
% This is a demo fucntion to act as a resource for the solving of systems
% of 1rst order ODE's. This particular example is a linear fox and rabbit
% populations as the PREDATOR vs. PREY model developed by Lotka and
% Volterra.
close all;
clear all;
clc;
%MAIN SCRIPT
a=1; b=0.5; c=0.75; d=0.25; h=0.05;
R0=2; F0=1; tspan=[0 30];
[t,y]=RK2(@(t,y) FR(t,y,a,b,c,d), tspan, [R0 F0],h);
plot(t,y, 'Linewidth', 1.8)
%% Function Scripts
% Here we will define the ODE and Runge-Kutta Scripts to calculate our t,y
% values.
%ODE Definition Function
function yp = FR(t,y,a,b,c,d)
yp(1) = a*y(1)-b*y(1)*y(2);
yp(2) = -c*y(2)+d*y(1)*y(2);
end
%Runge-Kutta 2nd Order Accuracy Function
function [t,y] = RK2(f,tspan,y0,h)
t = tspan(1):h:tspan(2);
y(1,:)=y0;
for n=1:length(t)-1
k1=f(t(n),y(n,:));
k2=f(t(n)+h,y(n,:)+h*k1);
y(n+1,:)=y(n,:) + 0.5*h*(k1+k2);
end
end

Mehmed Saad on 13 May 2020
Set ColorOrder of axes. Currently i am setting it to random, You can select your custom color
close all;
clear all;
clc;
%MAIN SCRIPT
a=1; b=0.5; c=0.75; d=0.25; h=0.05;
R0=2; F0=1; tspan=[0 30];
[t,y]=RK2(@(t,y) FR(t,y,a,b,c,d), tspan, [R0 F0],h);
%
ax = gca;
ax.ColorOrder = rand(10,3);hold on
plot(t,y, 'Linewidth', 1.8)
Michael McDermott on 13 May 2020
Thank you!
I figured out how to set the 'gca' with an array of RGB values.
ax = gca;
ax.ColorOrder = 1/255*[[51 61 62]; 2.2*[51 61 62]; 3.6*[51 61 62]]
Here the 2.2 and 3.6 multipliers just adjust the "shade" of the original color. Thank you again for the help!

R2019b

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