Doubt math

11 views (last 30 days)
Nuno
Nuno on 6 Apr 2011
Edited: Jenna on 23 Feb 2023
I have the next expression and my unknown is "I".
I = ICC - IR.*(2.718.^((V1+Rs*I)./(m.*VT))-1) - ((V1+Rs.*I)/Rp);
Exist any function im Matlab that resolve this expression without math methods?

Accepted Answer

Matt Tearle
Matt Tearle on 7 Apr 2011
OK, to expand on the cyclist's answer:
  1. rewrite your equation in the form f(I) = 0: ICC - IR.*(exp((V1+Rs*I)./(m.*VT))-1) - ((V1+Rs.*I)/Rp) - I = 0
  2. having defined all the constants (ICC, m, VT, etc), make a function of I using an anonymous function handle: f = @(I) ICC - IR.*(exp((V1+Rs*I)./(m.*VT))-1) - ((V1+Rs.*I)/Rp) - I;
  3. apply fsolve to f
Like Walter, I'm assuming 2.718.^foo really means e^foo, which, in MATLAB, should be implemented as exp(foo).
  13 Comments
Nuno
Nuno on 11 Apr 2011
This expression:
-(V1-(-LambertW(-Rs*IR*Rp*exp(Rp*(Rs*ICC+Rs*IR+V1)/(m*VT*(Rp+Rs)))/(-Rs*m*VT-Rp*m*VT))+Rp*(Rs*ICC+Rs*IR+V1)/(m*VT*(Rp+Rs)))*m*VT)/Rs
But, how do you transform the expression in this form?
Walter Roberson
Walter Roberson on 11 Apr 2011
I used a different symbolic package to get that, but it is likely that solve() like Tim showed should be able to handle it.

Sign in to comment.

More Answers (4)

Matt Fig
Matt Fig on 6 Apr 2011
What do you mean "without math methods?" MATLAB uses only math methods as far as I know...
  14 Comments
Image Analyst
Image Analyst on 12 Oct 2012
Or "ASSEMPDE".
Image Analyst
Image Analyst on 15 Oct 2015
A new funny one is "removecats" (in the Statistics and Machine Learning Toolbox). People have been trying to use it on youtube and Facebook videos.

Sign in to comment.


the cyclist
the cyclist on 6 Apr 2011
You could use the function "fzero" to solve this equation.
  1 Comment
Nuno
Nuno on 7 Apr 2011
But how fzero resolve this problem?

Sign in to comment.


Tim Zaman
Tim Zaman on 6 Apr 2011
I guess what you need is just a solver; for example you define
syms ICC IR V1 Rs m VT Rp;
solve('I = ICC - IR.*(2.718.^((V1+Rs*I)./(m.*VT))-1) - ((V1+Rs.*I)/Rp)')
-untested-
  4 Comments
Nuno
Nuno on 7 Apr 2011
Ups... I don't understand...
Walter Roberson
Walter Roberson on 7 Apr 2011
"How this works" is that the symbolic solver does pattern matching and determines that the expression matches a pattern that it knows how to solve. It then substitutes the components from your actual expression in to the general solution to the kind of problem that it has decided your expression is. It so happens that the pattern matched is one whose answer is expressed in terms of the Lambert W function. _Why_ the Lambert W function is the answer for those kinds of problems is a topic for a series of lectures in complex analysis.

Sign in to comment.


Jenna
Jenna on 23 Feb 2023
Edited: Jenna on 23 Feb 2023
Unfortunately, there is no built-in MATLAB function that can solve an equation like the one you have given without using any mathematical methods. However, MATLAB does have functions that can help you solve equations numerically using methods like Newton-Raphson or the Bisection method.
Here's an example of how you could use the fsolve function in MATLAB to solve your equation:
% Define the function you want to solve
fun = @(I) ICC - IR.*(2.718.^((V1+Rs*I)./(m.*VT))-1) - ((V1+Rs.*I)/Rp);
% Use fsolve to find the value of I that solves the equation
I = fsolve(fun, x0);
% Display the result
disp(['The value of I that solves the equation is ', num2str(I)]);
In this example, x0 is an initial guess for the value of I. You would need to define the values of ICC, IR, V1, Rs, m, VT, and Rp beforehand.

Community Treasure Hunt

Find the treasures in MATLAB Central and discover how the community can help you!

Start Hunting!