ode45 output

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Erik Mele 2012-2-10

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https://ww2.mathworks.cn/matlabcentral/answers/28694-ode45-output

编辑： Hongyang 2013-10-18

Hi, I'm having trouble getting a list of values from my function.

function dT=odefun(t,T)
global T1 ...etc
... etc
T2=T1*((P2/P1)^n_ex);
dT=zeros(3,1);
dT(1)=...etc
T1=T2;

How can I get ode45 to return a list of all calculated values for T1, as for dT(3,1) and not just the last value?

Thank you

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Andrew Newell 2012-2-10

I strongly suspect that you have written odefun incorrectly. You are using a global variable to make each evaluation dependent on the previous one, which is not good practice. If you could add a description of your problem to your question, we might be able to help you sort it out.

Erik Mele 2012-2-21

Thank you, I realize that I was using ode45 incorrectly. I am having trouble with a heat and mass transfer problem, where I have 3 differential equations I need to solve, as well as other equations dependent on the differential equations.

Instead of writing the other equations inside ode45, is it possible to create a for loop, and repeatedly using ode45 inside?

My code is now

for i=1:x

P(i+1)=(1+(0.5/x)*i)*10^5; %Pa%

Tny(i)=T_g(i)*((P(i+1)/P(i))^n_ex);

P2=P(i+1);

T2=Tny(i);

Y2=Y(i);

j=(i-1)*(time/x);

k=(i)*(time/x);

tspan=[j k];

Ti=[m_l(i) D(i) T_l(i)];

[t T]=ode45(@odefun3,tspan,Ti);

len=size(T)

m_l(i+1)=T(len(1),1);

D(i+1)=T(len(1),2);

T_l(i+1)=T(len(1),3);

T_g(i+1)=Tny(i)+(m_l(i+1)-m_l(i))*(h_ev/M)*(1/(cp_air*m_g(i)));

%Gas temperature%

m_g(i+1)=m_g(i)+(m_l(i+1)-m_l(i))*(time/x);

m_s(i+1)=m_s(i)+(m_l(i+1)-m_l(i))*(time/x); %Total steam mass%

Y(i+1)=(((m_s(i)+(m_l(i+1)-m_l(i)))/Mv)/((m_g(i)+(m_l(i+1)-m_l(i)))/M)); %Mole fraction vapor%

end

Y2 T2 and P2 are now global variables used inside ode45. I am concerned with the use of j and k, are theese time variables correct inputs for the ode45 equation?

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