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How can i plot the response of function as a vector ?

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Mallouli Marwa
Mallouli Marwa 2016-5-7
编辑： Azzi Abdelmalek 2016-5-7
Hi,
To resolve a secon order differential equation i do this function , but i have a problem when i want to plot xdot.
function xdot = equacte(t,x)
% Function file for mass with spring.
% Position is first variable, velocity is second variable,load is the third variable
freq=100; %frequency (Hz)
w=2*pi*freq;
m=0.0112;
k=262.8257 ;
teta =-4.40e+03;
cp= 1.8492*10^-7;
for rload =0:20:50000
A = [0,1,0;-k/m,0,-teta/m;(-teta/rload),0,-1/(rload*cp)];
B = [0;1/m;0];
f =sin(w*t);
xdot = A*x+B*f;
end
end
In the principle program :
[t,x]=ode45(@equacte,[0:0.0004:1],[0,0,0]);
xdot=equacte(t,x);
plot(t,xdot(:,1),'O',t,xdot(:,2),'r',t,xdot(:,3),'b');

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采纳的回答

Azzi Abdelmalek
Azzi Abdelmalek 2016-5-7
编辑：Azzi Abdelmalek 2016-5-7
What this line is doing? xdot=equacte(t,x) just write
[t,x]=ode45(@equacte,[0:0.0004:1],[0,0,0]);
plot(t,x(:,1),'O',t,x(:,2),'r',t,x(:,3),'b')
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Azzi Abdelmalek
Azzi Abdelmalek 2016-5-7
Ok, but like you did it, the loop has no effect, only the last value will be taken in account.
Azzi Abdelmalek
Azzi Abdelmalek 2016-5-7
编辑：Azzi Abdelmalek 2016-5-7
Your function should look like
function xdot = equacte(t,x,rload)
% Function file for mass with spring.
% Position is first variable, velocity is second variable,load is the third variable
freq=100; %frequency (Hz)
w=2*pi*freq;
m=0.0112;
k=262.8257 ;
teta =-4.40e+03;
cp= 1.8492*10^-7;
A = [0,1,0;-k/m,0,-teta/m;(-teta/rload),0,-1/(rload*cp)]
B = [0;1/m;0];
f =sin(w*t);
xdot = A*x+B*f;
end
Then call it in the loop
for rload=2000:20:2040
[t,x]=ode45(@(t,x) equacte(t,x,rload),[0 1],[0,0,0]);
figure;
plot(t(2:end-1),diff(x))
end

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