Calling function in fminsearch

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Yokuna
Yokuna 2022-10-22
评论： Steven Lord 2022-10-22
Ran in:
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 个评论
显示 1更早的评论
Torsten
Torsten 2022-10-22
编辑：Torsten 2022-10-22
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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采纳的回答

Steven Lord
Steven Lord 2022-10-22
Ran in:
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 个评论
Yokuna
Yokuna 2022-10-22
Thanks! But I need the initial value as the value obtained in previous iteration of solution.
So initialPoints are not predefined but calculated in each iteration.
Steven Lord
Steven Lord 2022-10-22
Ran in:
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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