Calling function in fminsearch

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Yokuna
Yokuna on 22 Oct 2022
Commented: Steven Lord on 22 Oct 2022
I want to call a function lamda to update initial value in fminsearch.
The initial value of lambda(1) =-1.
I want to update in lambda as lambda(i+1)=lambda(i)-0.01*(lambda(end)).
This computation of lambda should continue until lambda(end) < 0.01. I am not able to call function in fminsearch as FMINSEARCH accepts inputs only of data type double.
close all
clear all
clc
[optimal_lambda,cost] = fminsearch(@cost_lambda, @lamda)
a = optimal_lambda(1)
function cost = cost_lambda(lambda)
part_a = @(t,y)[-0.02*y(1); (y(2)/0.8)*(1/0.8)*exp(0.01*t)];
[t,y]=ode45(part_a, [0 10], [0.5,-1]');
cost = (1-(1/0.01)*(1-exp(-log((-1+(y(1)/0.8)^2)/(0.015*lambda(1)*exp(0.01*t)))))*(1-(y(1)/0.8))^2);
function lambda = lamda(lambda)
lambda(1)=-1;
i=1;
for lambda(end)<0.01
Invalid expression. When calling a function or indexing a variable, use parentheses. Otherwise, check for mismatched delimiters.

Error in connector.internal.fevalMatlab

Error in connector.internal.fevalJSON
lambda(i+1)=lambda(i)-0.01*lambda(end)
i=i++
end
end
end
  3 Comments
Torsten
Torsten on 22 Oct 2022
Edited: Torsten on 22 Oct 2022
What is the function "lamda" for ? "fminsearch" searches for a value of "lambda" such that the objective function becomes minimal. There is no reason to vary or prescribe lambda on your own. fminsearch will do this for you.

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Accepted Answer

Steven Lord
Steven Lord on 22 Oct 2022
If you mean you want to call fminsearch repeatedly with different initial points, call it in a loop.
f = @sin;
initialPoints = (0:0.5:10).';
solutions = zeros(size(initialPoints));
for k = 1:numel(initialPoints)
x0 = initialPoints(k);
solutions(k) = fminsearch(f, x0);
end
For ease of display I'll put the points in a table.
results = table(initialPoints, solutions)
results = 21×2 table
initialPoints solutions _____________ _________ 0 -1.5708 0.5 -1.5708 1 -1.5708 1.5 -1.5708 2 4.7124 2.5 4.7124 3 4.7124 3.5 4.7124 4 4.7124 4.5 4.7124 5 4.7124 5.5 4.7124 6 4.7124 6.5 4.7124 7 4.7124 7.5 4.7124
  2 Comments
Steven Lord
Steven Lord on 22 Oct 2022
Okay. I'll use randi to compute my initial points, but you could use another function. In fact you could (except when whichTrial is 1) look at results(whichTrial-1) to use the results from the previous run as x0 for this run.
ntrials = 10;
initialPoints = zeros(ntrials, 1);
results = zeros(ntrials, 1);
f = @sin;
for whichTrial = 1:ntrials
x0 = randi([-10 10]); % You could compute this however you want
initialPoints(whichTrial) = x0; % Record it
results(whichTrial) = fminsearch(f, x0); % Compute with it
end
Now show the results table.
t = table(initialPoints, results)
t = 10×2 table
initialPoints results _____________ _______ -5 -7.854 -8 -7.854 2 4.7124 -6 -7.854 10 10.996 10 10.996 9 10.996 1 -1.5708 10 10.996 -3 -1.5708

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