[Scilab-users] Fwd: Help modeling ODE system

[Michael J McCann]

Stephane is right, BUT please don't try to use "differentiators" in the 
analog-computer-like Xcos system, That's not the way the real world 
works. Numerical Solutions of differential equations are done by 
integration, as is invoked by the ode( ) function and by the underlying 
computation in Xcos which uses them too.
Mike.
=================
On 2014-09-15 12:03, Stéphane Mottelet wrote:
> Hello,
>
> Why use a cannon to kill a fly ? Maybe this would be easier like this :
>
> function dvdt=f(t,v)
>     dvdt=[0.01 -0.01;-0.01 0.01]*v;
> endfunction
>
> t=0:0.1:10;
> v=ode([10000;5000],0,t,f);
> plot(t,v)
>
> S.
>
> Le 15/09/2014 13:05, Berns Buenaobra a écrit :
>> You could simulate those in XCOS like an analog computation using
>> Differentiators and its inverse for the solution also multipliers by the
>> way.
>>
>> Berns B.
>>
>> On Sun, Sep 14, 2014 at 10:54 PM, Farid Afandiyev<faridafandiyev at gmail.com>
>> wrote:
>>
>>> Thanks Mehran! This is exactly what I want!
>>>
>>> Kind regards,
>>>
>>> Farid.
>>>
>>>
>>> On Sun, Sep 14, 2014 at 4:04 PM, A Khorshidi<akhorshidi at live.com>  wrote:
>>>
>>>> Farid Afandiyev wrote
>>>>> It looks like this
>>>>> dV1/dt = 0.01V1 - 0.01V2
>>>>> dV2/dt = -0.01V1 + 0.01V2
>>>>> V1(0) = 10000
>>>>> V2(0) = 5000
>>>>>
>>>>> I want to plot V1 and V2 against time t=[0:10]
>>>> Hi;
>>>>
>>>> You can use the scheme below to solve system of ODEs in Scilab:
>>>> //
>>>> function xdot = modelName(t,x)
>>>>      xdot = f(t,x) // where xdot and x are vectors
>>>> endfunction
>>>>
>>>> x0 = [x1(0) x2(0)... xn(0)]' // a vector of the initial conditions
>>>> t0 = initialTime // a scalar: initial time
>>>> tf = finalTime // a scalar: final time
>>>> t = linspace(t0, tf)// a vector: the times that you want a solution for
>>>>
>>>> x = ode(x0,t0,t,modelName);
>>>>
>>>> plot(t', [x(1,:); x(2,:); ... x($,:)]')
>>>> //
>>>>
>>>> And to really answer your question:
>>>>
>>>> function Vdot=model(t, V)
>>>>      Vdot(1) = 0.01*V(1) - 0.01*V(2)
>>>>      Vdot(2) = -0.01*V(1) + 0.01*V(2)
>>>> endfunction
>>>> V0=[10000 5000]';
>>>> t0=0;
>>>> t=0:0.1:10;
>>>> V = ode(V0,t0,t,model);
>>>> plot(t', [V(1,:); V(2,:)]')
>>>>
>>>> HTH
>>>> Mehran
>>>> _
>>>>
>>>>
>>>>
>>>>
>>>> --
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>>>> http://mailinglists.scilab.org/Scilab-users-Fwd-Help-modeling-ODE-system-tp4031148p4031151.html
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>>>> at Nabble.com.
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-- 
Dr.M.J.McCann,MJMcCann-Consulting

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