Solving Systems of Nonlinear Algebraic Equations in Matlab

[IntegratedDerivative]

thanks for the help!

[ceikit91]

I premise i did not understand what the guess is. I tried first with a simply system: x+2y=0 x-y=0 and i did this: function fcns=eqns2(z) x=z(1); y=z(2); fcns(1)=x.+2*y.; fcns(2)=x.-y.; end Then I wrote guess=[ 2 3]; in the console and result=fsolve(@eqns2,guess) Error: File: eqns2.m Line: 4 Column: 11 Unexpected MATLAB operator Error in ==> fsolve at 249 fuser = funfcn{3}(x,varargin{:}); Caused by: Failure in initial user-supplied objective function evaluation. FSOLVE cannot continue

[jakeblanchard]

@ceikit91

Get rid of the "dots" in your function. That is, try this:

fcns(1)=x+2*y;

fcns(2)=x-y;

There is not such thing as .;

[bangthatdrumb]

er without guessing...

[bangthatdrumb]

Is there a method to find ALL roots of a system of nonlinear equations?

[jakeblanchard]

@bangthatdrumb

No there really isn't. The problem is that there could be no solutions, 1 solution, or an infinite number of solutions. It's just too difficult to have a general solver find all solutions. If you restrict the problem to a particular type of equation, then there may be a way to narrow things down.

[bangthatdrumb]

@jakeblanchard i used continuation software XPAUTT and counted them manually, horay!

[jakeblanchard]

@bangthatdrumb

good news!

[amziadi]

Hey thanks for providing such an easy-to-follow explanation! You have helped me to solve a very non-linear (and non-nice :P) system of equations needed for my Air-Breathing Engines undergraduate class. Thank you again!

[jasonjohnson195]

Hello! Do you know how to solve as nonlinear system of ordinary differential equations?

I think it can be done using Runge - Kutta or Lotka-Volterra. Do you have something ready?

[jakeblanchard]

@jasonjohnson195

Yes. I have You Tube videos called

Solve Ordinary Differential Equations in Matlab

and

Solving Second Order Differential Equations in Matlab

I can't post links to these, so you have to search. I also have some written materials at

blanchard "dot" ep "dot" wisc "dot" edu

Go there and then click on the first link

Introduction to Matlab

[jasonjohnson195]

@jakeblanchard

Although I managed to solve it alone, I would like to say you a big thank you for all the videos you have posted in youtube. Especially the "using Simulink to Solve Ordinary Differential Equations" was really very helpful.

[talalissa88]

Hello !

I have five unknowns with five equations, and I followed every step you showed me. When I run the file, the Matlab gives me the following message:

??? Input argument "n" is undefined.

Can you help me?

[jakeblanchard]

@talalissa88

I would have to see your script. Can you send me the m-file? Send to blanchard "at" engr.wisc.edu