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Asked by pouya jamali on 19 Oct 2011

I have an Ordinary Differential Equation as follow: dv/dt-av^2-b=0 where a and b are constants how to solve this equation using Simulink?

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Answer by Fangjun Jiang on 19 Oct 2011

Your equation can be written as dv/dt=a*v*v+b.

Drag an Integrator block, the input is dv/dt, the output is v, use Constant block, Product block and Sum block to construct the equation and then you can run the simulation to solve the equation.

The solution is only numerical. You can vary the value of a, b and the initial value of v to see the effect.

pouya jamali on 19 Oct 2011

I do that but the result is :

Derivative input 1 of 'test/Integrator' at time 0.78539826055126438 is Inf or NaN. Stopping simulation. There may be a singularity in the solution. If not, try reducing the step size (either by reducing the fixed step size or by tightening the error tolerances)

What can I do with this error?

Fangjun Jiang on 19 Oct 2011

That probably means that based on your value of a, b, initial value of v and the simulation step size, the simulation is unstable, or it's a fact that the value of v is becoming ruminatively large. What is your a, b, initial v and simulation step size?

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