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From: Nellie rajarova on 4 May 2010 19:35
I need to solve a system of coupled nonlinear equations of the form:

a11*u(1)+a12*u(2)=0;
du(2)/dt= b11*u(1)+b12*u(3);
du(3)/dt= c11*u(1)+c12*u(2)+c13*u(3);

where u(1),u(2) and u(3) are unknowns whose values at t=0 is given.
a11,a12...b12..c11,c12... are constants and values are know. How do I use ode15s to solve this system.
From: Torsten Hennig on 4 May 2010 22:51
> I need to solve a system of coupled nonlinear
> equations of the form:
>
> a11*u(1)+a12*u(2)=0;
> du(2)/dt= b11*u(1)+b12*u(3);
> du(3)/dt= c11*u(1)+c12*u(2)+c13*u(3);
>
> where u(1),u(2) and u(3) are unknowns whose values at
> t=0 is given.
> a11,a12...b12..c11,c12... are constants and values
> are know. How do I use ode15s to solve this system.

Define a mass matrix M as
m(1,1) = 0
m(1,2) = 0
m(1,3) = 0
m(2,1) = 0
m(2,2) = 1
m(2,3) = 0
m(3,1) = 0
m(3,2) = 0
m(3,3) = 1
and the vector du of the right-hand side as
du(1) = a11*u(1)+a12*u(2)
du(2) = b11*u(1)+b12*u(3)
du(3) = c11*u(1)+c12*u(2)+c13*u(3)

Best wishes
Torsten.
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