Minimal example where you run two loops simultaneously, and programmatically stop/switch a for-loop or while-loop or update the information inside those loops, while they are executing.

I have a question related to parallel computing, how to run two loops simultaneously, and how to programmatically stop a for loop or update the information inside a while loop.

I'm writing a program that performs animal tracking (a rat/mouse) in an open field box, and sends pulse (voltage) data to a DAQ device based on the rat's current location. This is for optogenetics experiments.

The image acquisition and tracking code is done.

The pulse generation code is done.

My problem is that I cannot do both simultaneously.

The DAQ is a basic device that takes a single voltage value between 0.0 - 5.0 range. Generating a pulse requires constructing an array of voltage values and looping over them. A simple example...

      for v = 0 : .1 : 5

          DAQsend(v)

      end

Tracking the rat around an open field requires capturing images from a camera, locating the subject, and determining whether it's position is inside some ROI. This also requires a loop...

    for t = 1:1000

        im = getCamImage()

        roi = determineROI(im)

    end

As you can see both the tracking and the DAQ pulse generation require loops, where the DAQ loop would be nested inside the tracking loop...

    for t = 1:1000

        im = getCamImage()

        roi = determineROI(im)

        if roi == 1
            v = 1;
            while t < 1000
                DAQsend(voltageArray(v))
                v = v+1;
            end
        else
            DAQsend(0)
        end

    end

Unfortunately, this code does not allow me to continue generating pulses while updating the tracking information. I'm wondering if something like this is even possible...

    for t = 1:1000

        im = rand;

        if im > .99
            v = 1;
            while t < 1000
                disp(v)
                v = v+1; 
                pause(.1)
            end
        end

    end

Here is a more complete runnable example

So far I've been able to use the batch function in the parallel computing toolbox to run two loops simultaneously.

    daqjob = batch('DAQsend',1,{daqObject,voltageArray});

This allows me to perform animal tracking and generate a single pulse train on a parallel worker. However, I cannot update or stop this pulse train.

I would be appreciative and in awe of anyone could provide a minimal example where you run two loops simultaneously, and programmatically stop/switch a for-loop or while-loop or update the information inside those loops, while they are executing.

[Brad]

Here is a video I made (for a reddit user) to demo what I could accomplish using the batch function.

Answer 1

[Brad]

The problem is solved now using a timer method. If you're interested, I left notes in the comments section here about how it works.

Answer 2

[Joe Yeh]

for t = 1:1000
  im = getCamImage()
  roi = determineROI(im)
  if roi == 1
    v = 1;
    while t < 1000
      DAQsend(voltageArray(v))
      v = v+1;
    end
  else
    DAQsend(0)
  end
end

The above code doesn't work as you wanted it to because the program can't break from the while loop. When the program enters the while loop, the loop condition (t<1000) is always satisfied because it's never updated. Correcting the loop condition should solve this problem.

 for t = 1:1000
    im = getCamImage()
    roi = determineROI(im)
    if roi == 1
      v = 1;
      while v < 1000  % Send out 999 pulses
        DAQsend(voltageArray(v))
        v = v+1;
      end
    else
      DAQsend(0)
    end
  end

[Brad]

The above code is just an example of the issue. I'm aware that the code does not break from the while loop. I'm looking for an example of code that can run a while-loop and a for-loop simultaneously; where something can happen inside the for-loop that causes the while-loop to break or update its information.

[Karthik Sampathkumar]

hi Brad,

I require a similar solution. Have you found the solution for the problem, if yes could you share your ideas please.

Thank you