MATLAB: How to use fsolve on a function, where not all input arguments are to be varied

fsolve

Hi there,

let me pose the question in code. Lets assume we have a function:

y = test(a,b)

where a and b are vectors. now I want to solve the function test using fsolve, but only varying a and keep the vector b constant.

fsolve(@test,x0,options,…)

Thanks for any help,

DKP

Best Answer

I found a rather simple solution.

I defined b as global and. That worked fine for me.

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MATLAB: Optimisation toolbox error

The function you pass to lsqnonlin must accept a vector of values the same size as your starting point, and must return a vector of function values (possibly a different size.)

Have another look at your fit_simp_optim code: you use A and B and n but those are not defined as variables anywhere. (What happened to C, by the way?)

Redefine your code:

function diff = fit_simp_optim(ABn, X, Y)
    % This function is called by lsqnonlin.
    % x is a vector which contains the coefficients of the
    % equation.  X and Y are the option data sets that were
    % passed to lsqnonlin.
    A = ABC(1); B = ABC(2); n = ABC(3);
    diff = (A+B*(X.^n)) - Y;
end

Then code

X = xlsread('QS2T.xls',9,'V638:C1835');
Y = xlsread('QS2T.xls',9,'W638:W1835');
lb = [800;0;0];
ub = [1600;600;10];
StartAt = [800;1537;0.1448];
optABn = lsqnonlin( @(ABn) fit_simp_optim(ABn,X,Y), StartAt, lb, ub);

MATLAB: How to use syms variables in function

In order to do that, you will have to convert ‘A’ to a symbolic object as well:

function [A] = Test(a,b)
    A = sym('A',[1 2])
    A(1,1)=a+1;
    A(1,2)=b;
end

then:

Q = Test(0,b)
Q =
[ 1, b]

Best Answer

Related Solutions

MATLAB: Optimisation toolbox error

MATLAB: How to use syms variables in function

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