# How to solve a differential equations' system in SIMULINK

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Valentina on 8 Mar 2012
Commented: Nilecram on 29 Aug 2015
I need to solve a system of 5 differential equations that are characterized by the presence of the unknown variable both at the second member of the equation and in the derivative. I tried to use a block Discrete-Time Integrator with a loop that pick up the output of the block and calculate the second member of the equation and then enters again the integrator as dT/dt. I make an example:
cy' = ay + b --> with a gain block that multiply the output of the intergrator I calculate ay and with a Sum I obtain ay +b. Then I divide all by c and the input (that is y') goes to the integrator.
Is that correct, is that possible? The results are wrong, but I would know if is because of an error or if is due to a wrong usage of the Discrete-Time Integrator block. Someone said me that it isn't possible to solve a system of differential equatiin this way, using this simulink structure, but I would like to know your opinion.
Thank you very much to everyone answers.

Guy Rouleau on 9 Mar 2012
What you describe sounds correct. The following posts gives a good example of how to draw ODEs in Simulink:
Nilecram on 29 Aug 2015
I have a system of 3 ODE and I wanted to solve them with simulink. Could you please explain how to proceed? Thanks

sali on 4 Mar 2015
I want to do the same but I have 256 diff equations, can I use just Matlab blocks and call functions inside each other and at the end do the simulation?

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