how can I solve this equation by ode45 matlab code? Here z and zdot vary with time (t = 0:0.02:3) and simulation is also made for 3 seconds. My code gives answer different than that of Simulink model prepared for the same equation.Unable to figure out the reason or my matlab code is wrong? Matlab Code is attached in file.
Equation is :
dydt = (-lambda)*(abs(zdot))*(Y)*(abs(Y)^(n-1))-(beta)*(z)*(abs(Y)^n) + ((A)*(zdot));
where,z = 2*t^2 , zdot= diff(z)
Hi Pankaj,
Are you expecting this result?
It is simulated in https://octave-online.net/
function xdot = f(x, t)
xdot = zeros(1, 1);
lambda = 1;
beta = 0;
A = 1.5;
n = 2;
z1 = 2*t^2;
z2 = 4*t;
xdot(1) = - lambda*abs(z2)*x(1)*abs(x(1))^(n - 1) - beta*z1*abs(x(1))^n + A*z2;
endfunction
x0 = [0],
t = linspace(0, 3, 100);
y = lsode("f", x0, t);
plot(t, y)
Hi Pankaj,
Here is the attached file which contains the working code. Hope this helps
Thanks all for your reply. The Plot obtained by Simulink Model of the same equation is different than the given by Yew Chung Chak, Luis and Pratik.
The simulink model image and Graph obtained is attached here.
The simulink curve has maximum value of 1.5 whereas the suggested Matlab code has 1.2. This is the issue why the graph obtained by Simulink is different than obtained by Matlab Code.
Hi Pankaj,
Thanks for your update.
You could have stated your real question at the beginning. Be clear and concise in 'designing' your question so that interested readers can provide a simple and effective answer/solution to your question/problem.
Please check the circled parts. Carry out your due diligence to troubleshoot your Simulink model. You can place scopes to measure some signals to perform some logical tests.
Hi Yew,
Thanks for your valuable suggestion for correcting my matlab code as well as simulink model.
It's working perfectly.
Thanks all others too.
Hi Pankaj,
Good to hear that.
To be honest, your Simulink model looks a bit messy. Dr. Richard J. Gran, the author of Numerical Computing with Simulink, calls it "spaghetti Simulink model".
If you are unfamiliar with the Simulink blocks, you are advised to use the Fcn block under User-Defined Functions in the Simulink Library Browser and type out the differential equations manually as shown on the figure. Alternatively, you can use MATLAB built-in Differential Equations Editor (DEE) to automatically generate the Simulink model for uncomplicated system.
https://blogs.mathworks.com/simulink/2014/10/15/special-vintage-differential-equation-editor/
- Badges
- Science topic