You can use afterEach to automatically invoke functions on each of the results of parfeval computations.

Use parfeval to compute random vectors in the workers. With default preferences, parfeval creates a parpool automatically if there is not one already created.

for idx = 1:10
    f(idx) = parfeval(@rand, 1, 1000, 1);
end

Display the maximum element in each of those vectors after they are created. afterEach executes the function handle on the output of each future when they become ready.

afterEach(f, @(r) disp(max(r)), 0);

    0.9975

    0.9990

    0.9982

    0.9991

    0.9982

    0.9998

    0.9999

    0.9986

    0.9996

    0.9990

You can combine afterEach and afterAll to automatically invoke more functions on the results of futures. Both afterEach and afterAll generate future variables that can be used again in afterEach and afterAll.

Use parfeval to compute random vectors in the workers. With default preferences, parfeval creates a parpool automatically if there is not one already created.

for idx= 1:10
    f(idx) = parfeval(@rand, 1, 1000, 1);
end

Starting parallel pool (parpool) using the 'local' profile ...
connected to 8 workers.

Compute the largest element in each of those vectors when they become ready. afterEach executes the function handle on the output of each future when they become ready and creates another future to hold the results.

maxFuture = afterEach(f, @(r) max(r), 1);

To compute the minimum value among them, call afterAll on this new future. afterAll executes a function on the combined output arguments of all the futures after they all complete. In this case, afterAll executes the function min on the outputs of maxFuture after completing and creates another future to hold the result.

minFuture = afterAll(maxFuture, @(r) min(r), 1);

You can fetch the result using fetchOutputs. fetchOutput waits until the future completes to gather the results.

fetchOutputs(minFuture)

ans = 0.9973

You can check the result of afterEach by calling fetchOutputs on its future variable.

fetchOutputs(maxFuture)

ans = 10×1

    0.9996
    0.9989
    0.9994
    0.9973
    1.0000
    1.0000
    0.9989
    0.9994
    0.9998
    0.9999

You can perform asynchronous computations on workers using parfeval and leave the user interface responsive. Use afterEach to update the user interface when intermediate computations are ready. Use afterAll to update the user interface when all the computations are ready.

Create a simple user interface using a waitbar.

h = waitbar(0, 'Waiting...');

Use parfeval to carry out time-consuming computations in the workers, for example, eigenvalues of random matrices. The computations happen asynchronously and the user interface updates during computation. With default preferences, parfeval creates a parpool automatically if there is not one already created.

for idx = 1:100
    f(idx) = parfeval(@(n) real(eig(randn(n))), 1, 5e2); 
end

Compute the largest value in each of the computations when they become ready using afterEach. Update the proportion of finished futures in the waitbar when each of them completes using afterEach.

maxFuture = afterEach(f, @max, 1);
updateWaitbarFuture = afterEach(f, @(~) waitbar(sum(strcmp('finished', {f.State}))/numel(f), h), 1);

Close the waitbar when all the computations are done. Use afterAll on updateWaitbarFuture to continue automatically with a close operation. afterAll obtains the figure handle from updateWaitbarFuture and executes its function on it.

closeWaitbarFuture = afterAll(updateWaitbarFuture, @(h) delete(h), 0);

Show a histogram after all the maximum values are computed. Use afterAll on maxFuture to continue the operation automatically. afterAll obtains the maximum values from maxFuture and calls histogram on them.

showsHistogramFuture = afterAll(maxFuture, @histogram, 0);

When computations for future variables result in an error, by default, afterEach does not evaluate its function on the elements that failed. If you want to handle any errors, for example, you have a user interface that you want to update, you can use the name-value pair PassFuture. When set to true, the future variable is passed to the callback function. You can call fetchOutputs on it, process the outputs, and handle any possible errors.

Send computations to the workers using parfeval. With default preferences, parfeval creates a parpool automatically if there is not one already created. If your parfeval computations result in an error, the future variable errors, and its Error property reflects it.

errorFuture = parfeval(@(n) randn(n), 0, 0.5);
wait(errorFuture);
errorFuture.Error

ans = 
  ParallelException with properties:

     identifier: 'MATLAB:NonIntegerInput'
        message: 'Size inputs must be integers.'
          cause: {}
    remotecause: {[1×1 MException]}
          stack: [1×1 struct]

If you use afterEach on that future, the callback function is not evaluated on those elements in the future that errored. In the code below, the msgbox is not executed because the future errors.

afterEach(errorFuture, @() msgbox('Operation completed'), 0);

To handle futures that result in errors, use the name-value pair PassFuture when calling afterEach. The future variable is passed to the callback function instead of its outputs. Call fetchOutputs on the future variable, and process its outputs. If the future results in an error, fetchOutputs throws an error that you can catch and handle. The following code shows an error dialog box.

afterEach(errorFuture, @handleError, 0, 'PassFuture', true);

function handleError(f)
    try
        output = fetchOutputs(f);
        % Do something with the output
    catch
        errordlg('Operation failed');
    end
end