solve an equation by iterration

2016 10 8
2 个回答
更新时间：2016 10 11
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Hello everyone!
I haven't been using matlab for a while and I struggle on a simple equation.
I need to obtain this result: Sigma = solve( Sigma== Sigma0*(1+k*(Epsilon-Sigma/E))^n; ) All parameters sigma0, k, Epsilon, E and n=0.2; are known. The only reason for witch I need matlab is the fact that sigma (the unknown), is on both side of the equation, and I need a iterative solver.
I though about the ode45 function but I can not find a example that fit's what I want to obtain. if I am not mistaken, I can find the derivative of the function.
dSigma= -n*Sigma0*(1+k*(Epsilon-Sigma/E))^(n-1)*(k/E)
Can someone tell me the few lines required to solve this? Thank you!

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回答（2 个）

Massimo Zanetti
Massimo Zanetti 2016-10-8

2 个投票

Put Sigma in the other side of the equation by changing it sign, and then use fsolve. https://it.mathworks.com/help/optim/ug/fsolve.html

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Brice Thomas
Brice Thomas 2016-10-11
I still strugle, could you give a example of code? As I detailled in the answer.
Thank you!

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Brice Thomas
Brice Thomas 2016-10-8

0 个投票

Sorry, I struggled one hour one this simple problem without seeing the program works at the end of the day...
I decided to make a simple example to test the fsolve, but even here, it does not compile and give me my root.
Here is a screen-shot of the example and the code.
function [r] = H(X) % a general function that take imput: [0:0.01:4] and must give me the % roots of sine (X) on the interval.
function [ Y ] = Test1( X )
Y=(log(X)-2); plot(X,Y); end
function [Z]=Myroot(X) X0=0.3; Z=fsolve(Test1(X),X0) end
r=Myroot(X) end
My real problem requires only for me to find the root of the expression. For this I wanted to make a function and solve it. But as I said, I strugle. Maybe helping pointing what is wrong here will help me on the other problem.
Thank you!

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John D'Errico
John D'Errico 2016-10-8
Please stop adding answers every time you make a comment. This is not an answer. There is a button to make a comment. Use it.
Torsten
Torsten 2016-10-11
Use
Z=fsolve(@Test1,X0)
instead of
Z=fsolve(Test1(X),X0)
Best wishes
Torsten.

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Torsten
Torsten
2016-10-11

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