Ode15i problem

Hi, I am using ode15i to solve some implicit ODEs. I got 7 equations having the form: f(x1,x2,x3,x4,x5,x6,x7,x1',x2',x3',x4',x5',x6',x7')=0 Each of the equation cannot be ignored. Solving this set of equations is easy. But I need to add the following condition into the equations: x7=x3^2-x2*(x4-x2)=0

I have tried taking x3=sqrt(x2*(x4-x2)) into one of the 7 equation, but an error occurred. And the solution of X should not be complex.

Is there another way to add the condition into the ODEs?

Another question is how to use Jacobian in ODESET?

Answer 1

[Torsten]

Remove the original equation to determine x7 and replace it with the new one:

x7-x3^2+x2*(x4-x2) = 0

Best wishes

Torsten.

[Gary Li]

Each of the equation can not be replaced.

[Torsten]

Then your system can't be solved since you have 8 equations for 7 unknown functions.

[Gary Li]

It can be solved.8 equations, 7 unknown function. If there is 7 equations, 6 or less functions, it cannot be solved then

[Torsten]

Please include such a system with 8 independent equations for 7 unknown functions that can be solved.