How does a vectorized MATLAB / Optimization toolbox algorithm decide if X (output to objective function) is going to be a single point or several points?

How does a vectorized pattern search alghoritm decide if the X should be a single point or several points?

In the global optimization toolbox user's guide R2019b chapter:(4-111) there is the following text:

"Note Write your vectorized objective function or nonlinear constraint function to accept a matrix with an arbitrary number of points. patternsearch sometimes evaluates a single point even during a vectorized calculation."

I am interested in when/why pattern search only evaluates a single point instead of several?

I have looked in the user's manual for a more detailed explinatation but have not found one, maybe I have missed something?

-------------------------------- Example ------------------------------------

One simple example:

%% SimpleTest
ObjectiveFunction = @SimpleFunc;
options = optimoptions('patternsearch');
options = optimoptions(@patternsearch,'PlotFcn',{@psplotbestf}, ...
 'Display','iter');
InitialMeshSize_Data=1;
options = optimoptions(options,'UseVectorized', true);
options = optimoptions(options,'InitialMeshSize', InitialMeshSize_Data);
options = optimoptions(options,'UseCompletePoll', true);
options = optimoptions(options,'SearchFcn', @GPSPositiveBasisNp1);
options = optimoptions(options,'Display', 'off');

lb=[];
ub=[];
x0=ones(1,10);

[x, fval] = patternsearch(ObjectiveFunction,x0,[],[],[],[],lb,ub,[],options)

SimpleFunc

function  x_out = SimpleFunc(x_in)

    for i=1:size(x_in,1)
       X(i,:) = x_in(i,:).^3; % just takes the input value to the power of 3.
    end
    
    for ii=1:size(X,1)
        x_sum(ii) = sum(X(ii,:)); % sums the rows to and returns as the Value
    end
x_out=x_sum;
end

If I have a breakpoint in the start of SimpleFunc and study the incoming values from pattern search. The first 'run/iteration' gives a 2-by-10 matrix (good it tests two points), but then for all the other 'runs/iterations' it only gives me a 1-by-10 vector, which means one single point (right?).

Is there any way to make the input from pattern search always or more often give a matrix to the objective function?

best regards,

Markus

[Gifari Zulkarnaen]

If 'UseVectorized' is true, the incoming value supposed to be 2N/Np1-by-10 in your example. How do you set breakpoint and get the incoming values?

[Markus Lythell]

Hi! The values are sent to the objextive function in which there's a breakpoint before the parfor loop begins. Thank you for your reply, however I think my issue is solved.