# ODEs system

조회 수: 21 (최근 30일)
Andrea 2011년 7월 26일
i'm trying to solve this system of differential equations, can someone told me how to use the ODE45 function?
dPp/dz= Pp*gammap*(sigmape*N2 −sigmapa*N1)−α*Pp;
dPs/dz= Ps*gammas*(sigmase*N2 −sigmasa*N1)−α*Ps:
dPASE/dz=PASE*gammas*(sigmaSE*N2-sigmasa*N1)+2*sigmase*h*gammas*Vs*Δv-alfas*PASE;
with N1=ρ*(1+W12*t)/(1+(W12+W21)*t+R*t)
N2=ρ*(R*t+W21*t)/(1+(W12+W21)*t+R*t)
W12=[(sigmasa*gammas) / (h*Vs*A)](Ps+PASE) W21=[(sigmase*gammas) / (h*Vs*A)](Ps+PASE) R=[(Pp*gammap*sigmapa) / (h*Vp*A)](Ps+PASE)
(gammap,gammas,sigmase,sigmape,sigmapa,sigmasa,h,Vs,Vp,A,Δv,α,ρ are known parameters).

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### 채택된 답변

Arnaud Miege 2011년 7월 29일
Also, there seems to be 4 variables, not three. Below is the modified code I used and the results I get with your parameters. Again, check the values and the units.
Pp=y(1);
Ps=y(2);
PASE_plus=y(3);
PASE_minus=y(4);
W12=(((sigmasa*gammas)/(h*Vs*A))*(Ps+PASE_plus+PASE_minus));
W21=(((sigmase*gammas)/(h*Vs*A))*(Ps+PASE_plus+PASE_minus));
R=((Pp*gammap*sigmapa)/(h*Vp*A));
N1=(rho*((1+W21*t)/(1+(W12+W21)*t+R*t)));
N2=(rho*((R*t+W12*t)/(1+(W12+W21)*t+R*t)));
dydz(1)=Pp*gammap*(sigmape*N2-sigmapa*N1)-alfap*Pp;
dydz(2)=Ps*gammas*(sigmase*N2-sigmasa*N1)-alfas*Ps;
dydz(3)=PASE_plus*gammas*(sigmase*N2- ... sigmasa*N1)+2*sigmase*N2*gammas*h*Vs*deltav-alfas*PASE_plus;
dydz(4)=-PASE_minus*gammas*(sigmase*N2- ... sigmasa*N1)+2*sigmase*N2*gammas*h*Vs*deltav+alfas*PASE_minus;
And this is how I call the|ode| solver:
[z,y]=ode45('signalFW',[0 20],[10 0.001 0 0]);
figure(1),subplot(2,1,1),plot(z,y(:,1:2)),grid on,ylabel('Power in mW'),legend('Pp','Ps');
subplot(2,1,2),plot(z,y(:,3:4)),grid on,xlabel('length EDFA in m'),ylabel('Power in mW'),legend('PASE+','PASE-');
This gives me the following results:
Is that what you'd expect? If not, check the values of your parameters.
Arnaud
##### 댓글 수: 1이전 댓글 -1개 표시이전 댓글 -1개 숨기기
Andrea 2011년 7월 29일
Your results are the same as mine..maybe there is something wrong with the parameters. Thank you!

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### 추가 답변 (2개)

Arnaud Miege 2011년 7월 27일
Have a look at the examples provided in the documentation. You need to write a function that computes the derivatives of your variables as a function of time and the variables themselves, and pass this to the ode solver.
HTH,
Arnaud
##### 댓글 수: 11이전 댓글 9개 표시이전 댓글 9개 숨기기
Andrea 2011년 7월 28일
Can I send you an e-mail?
Arnaud Miege 2011년 7월 29일
Can you just upload an image of the equations and the results you expect for certain numerical parameters?

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Arnaud Miege 2011년 7월 29일
This is the results I get with your code:
##### 댓글 수: 2없음 표시없음 숨기기
Andrea 2011년 7월 29일
You can find the model and the result in these two articles (the correct model is in the second)
http://www.sendspace.com/file/uujskz
http://www.sendspace.com/file/c7abb0
Is my code correct (for the first iteration of the article's model?)
Arnaud Miege 2011년 7월 29일
The code looks correct if you refer to equations (1) to (9) of the paper. However, you should check that the units used for the various parameters are consistent, and that the numerical values make sense.

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