MATLAB: How to select an interval in fsolve

fsolveinterval

I am using fsolve to solve a set of two non linear equations in two variables. But I have no idea which interval I should select. Is there any way or procedure to guess the interval ? please help. Thanks.

Best Answer

It depends on the functions. If there is a global minimum (one unique solution), where you start will likely not be important. If you doubt that there is a global minimum, and if there could be several regional minima, use the Global Optimization Toolbox patternsearch function. The other option is to use a genetic algorithm. Even if you do not have the Global Optimization Toolbox, genetic algorithms are easy to write in MATLAB.

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MATLAB: How to plot two conditions together

Use logical indexing as described by the blog posts, videos, and documentation that this search on the Support website returns.

a = 1.5;
r = 0:0.01:2;
result = NaN(size(r));  
condition1 = r <= a;
result(condition1) = ... % use r(condition1) in place of r in this expression
condition2 = r > a;
result(condition2) = ... % use r(condition2) in place of r in this expression

Now plot using r and result.

MATLAB: Globalsearch not working for a function file.

Lets start by reading the error message: "Supplied objective function must return a scalar value"

So, the objective function must return a scalar value. A scalr has size 1x1. Lets run the objective function and see if it returns a scalar value:

>> X = Trans_eqn_taperedfiber([1/3,2/3]);
>> size(X)
ans =
         1       49000

Is 1x49000 scalar? No. So the problem is your function returns a vector, which both the documentation and the error message clearly state is not allowed. You need to change your function to return a scalar value. Also note that you could generate a, b, and c without the loop using simpler vectorized code.

Best Answer

Related Solutions

MATLAB: How to plot two conditions together

MATLAB: Globalsearch not working for a function file.

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