[R] Differential problem

[Berend Hasselman]

On 11-07-2013, at 12:05, Raphaëlle Carraud <raphaelle.carraud at oc-metalchem.com> wrote:

> Sorry,
> 
> Here is the program I have until now:
> 
> reaction<-function(z, state, dval, parameters) {
>  with(as.list(c(state)),{
> 
>    K2 <- 10^(2993/Tr-9.226)*(10^-3)       
>    K3 <- 10^(2072/Tr-7.234)*(10^-3)
>    K4 <- 10^(-20.83/Tr-0.5012)
>    K5 <- 10^(-965.5/Tr-1.481)
>    k1 <- (10^(652.1/Tr-0.7356))*(8.314*Tr/P)^2
>    kf2 <- 1.4*10^-33*(Tr/300)^(-3.8)*6.022*10^23*10^-6
>    kb2 <- kf2/K2*P/(8.314*Tr)
>    kf3 <- 3.1*10^-34*(Tr/300)^(-7.7)*10^(-6)*6.022*10^23
>    kb3 <- kf3/K3*P/(8.314*Tr)
>    kf4 <- 41
>    kf5 <- 0.25
> 
>    r1 <- k1*A^2*H
>    r4 <- kf4*D*G - kf4/K4*E^2
>    r5 <- kf5*C*G - kf5/K5*E*I
> 
>    res1 <- -dA + dB + 2*dC - 2*r1 - 2*r5          
>    res2 <- dA + dD + r1 + r4                     
>    res3 <- K2 - C/B^2                             
>    res4 <- K3 - D/(A*B)                           
>    res5 <- r5 + 2*r4 - dE           
>    res6 <- r5 -dI                 
>    res7 <- -r5 - r4 - dG             
>    res8 <- -r1/2 - dH                
> 
>    list(c(res1, res2, res3, res4, res5, res6, res7, res8))
>  })   # end with(as.list ...
> }
> 
> Ti <- 273+90      #K
> Pt <- 0.98*10^5   #Pa
> 
> xi <- c(0.3,   #x_NO
>        0.1,   #x_NO2
>        0,     #x_N2O4
>        0,     #x_N2O3
>        0.05,  #x_HNO2
>        0.05,  #x_HNO3
>        0.2,   #x_H2O
>        0.3)   #x_O2
> 
> state <- c(A = xi[1]*Pt,
>           B = xi[2]*Pt,
>           C = xi[3]*Pt,
>           D = xi[4]*Pt,
>           E = xi[5]*Pt,
>           I = xi[6]*Pt,
>           G = xi[7]*Pt,
>           H = xi[8]*Pt)
> 
> dval <- c(dA = 1,
>          dB = 1,
>          dC = 0.5,
>          dD = 0.2,
>          dE = 0,
>          dI = 0,
>          dG = 0,
>          dH = 0)
> 
> parameters <- c(Pt = 0.98*10^5)
> 
> z <- seq(0, 1, by = 0.01)  
> 
> library(deSolve)
> out <- daspk(y = state, dy = dval, times = z, res = reaction, parms = 0)
> head(out)
> plot(out)
> 


When I run this I get this error message:

Error in eval(expr, envir, enclos) : object 'Tr' not found

And shouldn't the first line of the reaction function be this

with(as.list(c(state,dval,parameters)),{

in stead of this

with(as.list(c(state)),{

The call of daspk also seems incorrect; shouldn't it be

out <- daspk(y = state, dy = dval, times = z, res = reaction, parms = parameters)

And finally: where does variable P come from? Not defined anywhere!

Berend


> -----Message d'origine-----
> De : Berend Hasselman [mailto:bhh at xs4all.nl] 
> Envoyé : jeudi 11 juillet 2013 11:18
> À : Raphaëlle Carraud
> Cc : r-help at r-project.org
> Objet : Re: [R] Differential problem
> 
> 
> On 11-07-2013, at 09:13, Raphaëlle Carraud <raphaelle.carraud at oc-metalchem.com> wrote:
> 
>> Hello,
>> 
>> I have the following differential equation system to solve, the variables I wish to obtain being A, B, C, D, E, I, G and H.
>> 
>>   0 = -dA + dB + 2*dC - 2*r1 - 2*r5
>>   0 = dA + dD + r1 + r4
>>   0 = K2 - C/B^2
>>   0 = K3 - D/(A*B)
>> 
>>   0 = r5 + 2*r4 - dE
>>   0 = r5 -dI
>>   0 = -r5 - r4 - dG
>>   0 = -r1/2 - dH
>> 
>> r1, r4 and r5 are variables expressed as functions of A, B, C, D, I, G and H, calculated previously in the integrated function. K2 and K3 are parameters.
>> 
>> As I have two algebraic equations, I think this system is a DAE (Algebraic differential equation). I found in the package deSolve two functions that resolve DAE but I didn't manage to obtain a solution; it says that the variable dA cannot be found.
>> 
> 
> Show us your script where you define the function and run the DAE solver. Without that nobody can provide an answer.
> 
> Berend.
> 
>> Does anyone know how to solve this problem?
>> 
>> Thank you
>> 
>> Raphaëlle Carraud
>> 
>> 
>> Raphaëlle Carraud
>> 
>> 	[[alternative HTML version deleted]]
>> 
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>