Solving non-linear equation including natural logarithm

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Ogulcan Acikgoz 2019-11-20

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https://ww2.mathworks.cn/matlabcentral/answers/492224-solving-non-linear-equation-including-natural-logarithm

评论： Ogulcan Acikgoz 2019-11-21

Hi guys, I am trying to solve this eqn for y and I am just waiting, Matlab stays busy for some reason. What can I do? Do you think there is a simple way to do it?

syms a b c x y
eqn = (1/b) * (c-y)^(3/2) == a-x-(1/2)*log(1-y/c) 
eqn=rewrite(eqn,'log')
s=solve(eqn,y,'IgnoreAnalyticConstraints',true)

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Jeremy 2019-11-20

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编辑：Jeremy 2019-11-20

Most probably, there is no analytical solution for y in terms of (a,b,c,x). You can solve numerically for y at given values of a,b,c,x by using fzero.

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Jeremy 2019-11-20

I would solve for x such that

x = @(y) a - (1/b) * (c-y)^(3/2) - (1/2)*log(1-y/c);

and do a regression for x in terms of a,b,c,y?

Ogulcan Acikgoz 2019-11-21

It seems a good idea, thank you. I am sure it is very easy but I tried to solve and I could not manage to write the code for regression. Also I tried to use curve fitting toolbox and it gave me an error saying that it is too complex.

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