solve an equation by iterration

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!

Answer 1

[Massimo Zanetti]

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

[Brice Thomas]

I still strugle, could you give a example of code? As I detailled in the answer.

Thank you!

Answer 2

[Brice Thomas]

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!

[John D'Errico]

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]

Use

Z=fsolve(@Test1,X0)

instead of

Z=fsolve(Test1(X),X0)

Best wishes

Torsten.