How can I define boundary conditions using lsqnonlin solver?

Hi everyone,

I am trying to solve an equation: K * u = q(u)

where q is a function of u. For this reason I formed an error-loading vector: qerr(u) = K * u - q(u)

I am using a lsqnonlin solver. I am trying to implement boundary conditions by setting certain elements of u vector to 0.

I scanned the mathworks but I cannot find a solution to this problem.

Thank you for your help!

Answer 1

[Fernando]

First I'd suggest you to create an m-file to evaluate your error vector.

% Example for that function:

function Error = CostFunction(Unknowns)

% Unknowns can be a vector, so you can extract it like this:

a = Unknowns(1);

b = Unknowns(2);

% Compute the Error here.

% End of m-file

Now in your main m-file you can define the initial conditions for your unknowns:

Unknowns = [1, 0, 4]; % 3 variables in this example

options = optimset(' .... ', ' .... '); % your solver options goes here

UnknownsLB = [0, -5, 2]; % lower bound definition

UnknownsUB = [2, 5, 10]; % upper bound definition

x = lsqnonlin(@CostFunction,Unknowns,UnknownsLB,UnknownsUB,options) % solve it!