Setting up ODE in Matlab for ODE 45 solver

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DIP 2017-3-6

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https://ww2.mathworks.cn/matlabcentral/answers/328322-setting-up-ode-in-matlab-for-ode-45-solver

编辑： DIP 2017-3-8

Hi, I am having difficulty setting this problem up for the ODE45 solver. It is a kinetics equation, relating R (rate constants as a function of concentrations C), T (Temperature) and h (heat of formation) all of which vary with distance x. There are 3 species that take part in the reaction.

How do I formulate the function that calculates all these parameters to call in the ODE45 solver ( something like dTdx = .... ) How to plot x,T and x,C (what would be the correct syntax to plot these). Any help with a pseudo code will be greatly appreciated.

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DIP 2017-3-7

Hi Torsten, I am getting matrix dimension errors.

DIP 2017-3-7

编辑：DIP 2017-3-7

在 MATLAB Online 中打开

hi Torsten, there are only 2 ODEs
dC/dx=R
dT/dx=RH
R and H are functions of T and C. R and C are arrays.

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采纳的回答

Torsten 2017-3-7

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https://ww2.mathworks.cn/matlabcentral/answers/328322-setting-up-ode-in-matlab-for-ode-45-solver#answer_257616

在 MATLAB Online 中打开

function dydx = hw2_5(x,y)
C(1) = y(1);
C(2) = y(2);
C(3) = y(3);
T    = y(4);
% Constants
A  = 2.2e10;
Ea = 130000;
Ru = 8.3145;
rho=1.3;
cp=1200;
u=1.5;
% Rate Constants and heat of formation
h(1)=-110530;
h(2)=0;
h(3)=-393520;
R(1)     = -A * (exp(-Ea /(Ru*T))) * C(1) * sqrt(C(2)); 
R(2)     = 0.5 * R(1);  
R(3)     = -R(1);
dTdx=-(R(1)*h(1)+R(2)*h(2)+R(3)*h(3))/(cp*rho*u);
dydx = [R(1);R(2);R(3);dTdx]