MATLAB Answers

## Set of ODEs with an additional condition

Asked by Ghazwan

### Ghazwan (view profile)

on 23 Oct 2016
Latest activity Answered by Torsten

### Torsten (view profile)

on 28 Oct 2016
Accepted Answer by J. Alex Lee

### J. Alex Lee (view profile)

Hello, Let's say we have the following system of equations: x'=x+sin(y) y'=y+x And we know the boundary conditions. Also, we have the following condition that must be met in the solution of the two equations: log(x)+exp(x)-2*sin(y^2)=0 Is there an official title for this kind of problems? How to solve this system? Thank you!

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## 2 Answers

Answer by J. Alex Lee

### J. Alex Lee (view profile)

on 26 Oct 2016
Accepted Answer

I think this is a differential algebraic equation (DAE)?
Documentation for ode15s might help.

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Answer by Torsten

### Torsten (view profile)

on 28 Oct 2016

The two differential equations uniquely determine x and y. So you can't expect the algebraic relationship
log(x)+exp(x)-2*sin(y^2)=0
to be satisfied for the solution of the two differential equations
x'=x+sin(y) , y'=y+x.
Best wishes
Torsten.

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