ODE with discrete, external input

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Mario Trevino
Mario Trevino il 5 Apr 2011
Commentato: Torsten il 3 Nov 2014
Hi everybody, I want to solve a simple ODE for specific discrete time points in which constats are updated externally for each specific t value. vgr
t=1:100; dy/dt=kt;
where k is a external vector with length=length(t) and wich is considered in the equation for each t.... any help? thanks in advance

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Arnaud Miege
Arnaud Miege il 5 Apr 2011
Look at the third example on the ode solver documentation.
HTH,
Arnaud
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Mario Trevino
Mario Trevino il 5 Apr 2011
thanks, I found the same hint in the ode faqs.
It works
Sergio
Sergio il 31 Ott 2014
Hi Arnaud Miege, what would you suggest if the discrete ODE is a (2x2) system? Expanding the first question
t=0:0.02:1;
dxdt = Constant*K1;
dydt = Constant*K2;
where K1 and K2 are both external vector with length=length(t)? and both depending of two variables (x,y)?
Interp1 from matlab would be wrong since we would be interpolating in one dimension while the system is 2D.

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Torsten
Torsten il 31 Ott 2014
Use
http://www.mathworks.de/help/matlab/ref/griddata.html
if K1 and K2 don't depend explicitly on t, but on the dependent variables x and y.
Best wishes
Torsten.
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Sergio
Sergio il 31 Ott 2014
Modificato: Sergio il 31 Ott 2014
Thanks! but I still don't understand! Sorry!
I have another example here which is more easier but which can help me to understand.
Assume I have:
x1 = 40:0.005:55;
x1=x1';
x2=40:0.005:55;
x2=x2';
And then I discretize the following function:
V1=x1.*(0.2-0.005*x2);
V2=x2.*(-0.5+0.01*x1);
How can I use griddata now? And how can I solve this as an ODE?
Torsten
Torsten il 3 Nov 2014
Sorry, but meanwhile, I don't understand what you are trying to do.
Please specify more clearly:
What is the ODE you are trying to solve ?
Which MATLAB program are you trying to use to solve your ODE ?
Which kind of external input data do you have and where do they enter the ODE ?
Best wishes
Torsten.

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