How to solve a logarithmic equation?

I need to solve the equation 7X*log(X)-2=0 in matlab where 0<X<1. How such equations are solved through MATLAB? I have used fsolve single variable and there was no answer with an error message of: Optimization running. Objective function value: 0.0 Zero find terminated.

Réponses (2)

Torsten
Torsten le 24 Oct 2017
Modifié(e) : Torsten le 24 Oct 2017

2 votes

X = exp(lambertw(2/7))
Plot the function and you will see that there is no root for 0<X<1.
Best wishes
Torsten.

3 commentaires

Hanif Malekpoor
Hanif Malekpoor le 24 Oct 2017
Actually there is a root for this function near 0.64
Jan
Jan le 24 Oct 2017
There is a root for @(x) real(7*X*log(X)-2) at -0.6398364478 and one at 1.255537045

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Jan
Jan le 24 Oct 2017
Modifié(e) : Jan le 24 Oct 2017
No, no root here:
x = linspace(0,1,1000);
plot(x, 7 * x .* log(x) - 2);
Of course this is not a proof. But you can show easily, that 7*x*log(x) is smaller than 0 inside [0,1] such that subtracting 2 can never lead to a 0.

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Jan
le 24 Oct 2017

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