How to solve a nonlinear system of n equations
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Hi, I solved a nonlinear system of n equations using fsolve and it succeeded. But I couldnt solve another nonlinear system using fsolve. In fact it worked but its giving me wrong answers. I sent an email to mathworks but had no reply. Can Anyone help plz ?
2 Comments
Michael Haderlein
on 14 Oct 2014
Knowing nothing about your system of equations, it's impossible to say anything. Please give details about the equations and show the code which resulted in wrong values. Also, write how you know the correct results.
Answers (3)
Alan Weiss
on 14 Oct 2014
Your function is not smooth--it has both abs and sign calls. Therefore you cannot expect fsolve to work effectively starting from every point.
For more help, see fsolve could not solve the equation, which basically says that for this kind of problem you have to start from a wide variety of points.
Good luck,
Alan Weiss
MATLAB mathematical toolbox documentation
Matt J
on 14 Oct 2014
Edited: Matt J
on 14 Oct 2014
In view of how difficult your equations are, and because there are only 3 unknowns, I would just use exhaustive search, but in a multiresolution way. Start by sampling F(x1,x2,x3) on a coarse grid,e.g. with
[x1,x2,x3]=ndgrid(0:.1:10);
Evaluate F at all points on this grid (using vectorization, of course) and use min() to find the least norm(F) over all points. Then create a finer grid in the near neighborhood of the approximate solution and repeat...
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Alex Sha
on 11 Dec 2019
some results:
1:
x1: 1.04727193704753
x2: 2.09481403258296
x3: -3.14176920919256
2:
x1: -1.04719783053703
x2: 4.76397520013691E-7
x3: 1.04719557784678
3:
x1: -1.04722327842385
x2: -1.0469722124015
x3: 3.14151227631221
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