# How to solve a cubic equation using Genetic Algorithms?

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Nick on 20 Apr 2021
Commented: Walter Roberson on 20 Apr 2021
Hello there,
I want to write a code in matlab that finds a real solution for the equation x^3+x^2+x+7=0 , -5<x<5, using Genetic Algorithms.
How can I implement that with code?

Stephan on 20 Apr 2021

Walter Roberson on 20 Apr 2021
Edited: Walter Roberson on 20 Apr 2021
f = @(x) x.^4-2*x.^3+3*x.^2+x-4
f = function_handle with value:
@(x)x.^4-2*x.^3+3*x.^2+x-4
target = 5;
residue = @(x) (f(x)-target).^2
residue = function_handle with value:
@(x)(f(x)-target).^2
[bestx, fval] = ga(residue, 1)
Optimization terminated: average change in the fitness value less than options.FunctionTolerance.
bestx = -1.1833
fval = 0.5017
roots([1, -2, 3, 1, -4-target])
ans =
0.7541 + 1.9406i 0.7541 - 1.9406i 1.7076 + 0.0000i -1.2159 + 0.0000i
##### 2 CommentsShowHide 1 older comment
Walter Roberson on 20 Apr 2021
One that computed the left hand side of that polynomial, with the target set to the constant that is the right hand side of the equation.
... you are obviously answering homework, so I deliberately showed you how to do it for a different polynomial, so that you would have to do at least minimal study of the technique instead of just copying what I posted.

R2017b

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