Solving Systems of Nonlinear Algebraic Equations in Matlab

This video demonstrates how to solve nonlinear systems of equations in matlab. It is similar to root finding, but for multiple variables. The video can also be accessed at http://blanchard.ep.wisc.edu/ These videos were recorded for a course I teach as part of a distance masters degree. See http://mepp.engr.wisc.edu

Category:

Science & Technology

Tags:

• Matlab
• nonlinear
• algebraic
• equations

[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]

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!

[IntegratedDerivative]

thanks for the help!

[bangthatdrumb]

er without guessing...

[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]

@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.