plot from inside of function in parallel worker

hi, i am running some function (fun1) parallel using spmd and i want to plot values that are calculated inside of fun1. I want to display the values in a single plot, using a custom plot function (PlotFun). The problem is that i can not use "send" directly inside the spmd environment. This has to happen from within fun1.

The problem is that fun1 does not recognise the DataQueue that i have set up earlier. And if i refer to it using "gcp", it still has problems but then regarding the send function.

This would not be a problem if i could use the "send" function directly inside spmd. The reason for this quite weird circumstance is that i want to plot some values inside an objective function that is being evaluated by a solver running in parallel mode. This is resembled by the following simplified example:

clear, clc;

% initialize plot function and create figure
PlotFun([], "INIT")

D = parallel.pool.DataQueue;
D.afterEach(@(x) PlotFun(x, "ADD")); % add value after each evaluation

spmd
    
    % option a:
    fun1;

    % % option b:
    %send(D, fun1);
end


function out = fun1

    % option a:
    send(gcp, 1);
   
    % % option b:
    %out = 1;
end


function PlotFun(x, UseMode)

persistent f;
persistent i;
if UseMode == "INIT"
    f = figure;
    i = 1;
    return
end

if UseMode == "ADD"
    set(0, 'CurrentFigure', f);
    hold on
    plot(i, x, 'bo')
    hold off
    i = i+1;
    return
end

end

i out-commented option b. It does work, but i can not have the "send" there since that is hidden from me inside the solver file.

Answer 1

[Walter Roberson]

Enhanced to support plotting multiple points at the same time.

In the current version, the x axis location becomes the same as the order that the values happen to be returned; you could certainly change that, such as having fun1 return two columns with x and y values

% initialize plot function and create figure
PlotFun([], "INIT")

D = parallel.pool.DataQueue;
D.afterEach(@(x) PlotFun(x, "ADD")); % add value after each evaluation

spmd
    % % option b:
    send(D, fun1());
end

function out = fun1
    out = labindex * 10 + randi(9);
end

function PlotFun(y, UseMode)

    persistent AL AX i
    if UseMode == "INIT"
        f = figure;
        AX = axes('Parent', f);
        AL = animatedline('Parent', AX, 'color', 'b', 'Marker', 'o');
        i = 0;
        return
    end

    if UseMode == "ADD"
        xvals = i + 1: i + length(y);
        addpoints(AL, xvals, y);
        i = xvals(end);
    end

end