# system of 1st and 2nd order differential equations ode45

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gorilla3 on 16 Oct 2017
Edited: gorilla3 on 24 Oct 2017
I have a system of two 1st order diff eq and one 2nd order diff eq. I want to solve them simultaneously using ode45 and subsequently sum the solutions. I'm having troubles formulating the code for the 2nd order equation. Could you help? The code is:
Fx=@(t,xqxcxm)[ (-xqxcxm(1)+G_q .*(q-q_b)./q_b)./tau_q ;
(-xqxcxm(2) +0.3+3.*tanh(Pa_co2./Pa_co2_b -1.1))./tau_co2 ;
%insert 2nd order diff: xm'' = (-tau2* xm' -xm)/tau1^2 ]
[t, xqxcxm]=ode45(F,[0 100], [0 0 0]);
xq= xqxcxm(:,1);
xc= xqxcxm(:,2);
xm= xqxcxm(:,3);
x=xm+ xc -xq;
##### 2 CommentsShowHide 1 older comment
gorilla3 on 24 Oct 2017

Josh Meyer on 16 Oct 2017
The documentation explains how to express higher-order equations as first-order equations: Higher-Order ODEs
gorilla3 on 24 Oct 2017
Hello,
here is a better definition of my question. Could you please help me? I believe I formulated one of the equations erroneously.