How to plot specific variables rather than all of them?

Question

Brilliant Purnawan 2020-10-15

0
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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/614908-how-to-plot-specific-variables-rather-than-all-of-them

编辑： Ameer Hamza 2020-10-15

Hi, quite new to MATLAB and ran into some problems with plotting a specfici variable. Below the code is for the dynamics of a pendulum, made by Steve Brunton. My problem here is that I can't seem to refer to a certain variable, everytime I try to it just plot me all the graphs. Refer to the plot below, as you can see it plots all the variable within the function file, and If I try to plot only one part of it, it just return me an error message. See below for the full code.

This is the function file code:

function dx = PendEx(x,m,M,L,g,d,u)
Sx = sin(x(3));
Cx = cos(x(3));
D = m*L*L*(M+m*(1-Cx^2));
dx(1,1) = x(2);
dx(2,1) = ((m*L*g*Sx*Cx)-u*L+d*x(2)*L-m*L^2*x(4)^2*Sx)/(-(M+m)*L+m*L*Cx^2);
dx(3,1) = x(4);
dx(4,1) = (u*Cx-d*x(2)*Cx+m*L*x(4)^2*Sx*Cx-g*Sx*(M+m))/(L*(-M-m+m*Cx^2));

This is the script, as you can see the plot above is generated from just using the plot(y); I have alrady tried plotting certain the variables specifically but its not working. So any help is appreciated. My overall plan is to change the four plots into 4 different graphs. Thanks!

clear all, close all, clc
m = 0.25;
M = 0.635;
L = 0.5;
g = -10;
d = 1;
tspan = 0:.1:50;
y0 = [0; 0; pi; .5];
[t,y] = ode45(@(t,y)PendEx(y,m,M,L,g,d,0),tspan,y0);
plot(y);