Matlab App Designer: Index exceeds matrix dimensions error

I'm trying to take 4 sensor signals from Arduino to Matlab. The signals are read until the user decides to end the process (a button on the App). The signal comes into Matlab as a string where it is then split (0.1,0.2,0.4,0.5,1.2 to 0.1 0.2 0.4 0.5 1.2).

I'll try to condense the code to just one signal. I keep getting the "Index exceeds matrix dimensions" error. My code is also running very slow, so any tips on this would be greatly appreciated.

My Arduino code is fine. It's running as a switch case: when 's' is sent, the signal is read; when 'd' is sent, the program jumps out of that Arduino loop and no longer sends the signal. Without Matlab, it outputs exactly what I need it to.

Programs: MATLAB R2017a, App Designer, Arduino 1.8.2

Matlab App Code:

    char s; %Send to Arduino to start readings

    counter = 1;

    char d; %Send to Arduino to stop readings

    app.EndTest = 0;

    app.S1 = zeros(1, app.timer); %app.timer is set by user

    array1 = zeros(1, app.timer); %I tried to preallocate app.S1 and array1 to speed up the code

    while app.EndTest == 0

       data = fscanf(app.s, '%s'); %Gives all data in string

       IncomingString = split(data, ','); %Splits the string

       app.S1 = IncomingString(1); %Load Cell 1 is set to the first column values

       arrayString1 = str2double(app.S1); %Converts the ordinary array to a double

       app.S1EditField.Value = arrayString1; %Print Signal 1 value

       S1Time = arrayString1(counter); %This is where the index exceeds dimensions error comes up

       app.realGraph = plot(app.RealTimeAxes,timeData, arrayString1, 'b'); %Graph the result

       drawnow;

       counter = counter + 1;

       fprintf(app.s, 'd'); %Sends 'd' to Arduino to stop reading

    end

I have this code for 4 sensors (basically it just repeats everything four times). I know this code will not be able to copy and paste because it's in App Designer, but if you see anything that could help that would be awesome.

Thanks ahead of time!

[Tyler Kirsten]

Funny I'm having a very similar problem, doing basically the same thing, reading in sensor data from device over UDP and converting and storing it in an array for future access. thing is I also declared my array as you did with receiveValues = zeros(1, 7). And I manually index each element last being receiveValues(7), but still get the same error you do. I'm running a few timers though calling functions so app basically freezes each time. If you come up with something let me know and I'll do the same. Good luck!!

Answer 1

[Freya H]

What format/size does the arrayString1 variable have?

My best guess would be that in "app.S1 = IncomingString(1);" you possibly select a single string and then convert this to double which would end up in arrayString1 being a single value and not an array.

[Chandler Clark]

app.S1 is a single value (after the string is split). arrayString1 is then a double (same value as app.S1, just different type). S1Time is an array of all the values based off of a timer set. Should I set the size for S1Time as well?

Thanks for your quick response Freya!

[Freya H]

Since arrayString1 is a double (and not an array) Matlab can't process the statement arrayString(1) and says it exceeds dimension. The correct call would just be S1Time = arrayString1;

If you want to generate an array of all those different arrayStrings you could do the following:

S1time(counter) = arrayString1;

This will generate a warning and suggest to preallocate. To do so you can create S1time before the while-loop such as:

S1time = zeros(1,100);

[Dennis]

arrayString(1) should not be a problem, Matlab has no problem in returning the first entry of a scalar. However accessing arrayString(2) will throw an error.

A few questions from my side:

1. What is S1time? It appears that you are not using it, even if you could increment arrayString(counter) you would overwrite S1time in every iteration.
2. You are sending 'stop reading' in every loop iteration, but your start reading is outside the loop, this seems a bit odd to me.
3. What is the exit condition of your loop? app.EndTest never gets updated - so it will run infinite (or until it throws an error)
4. You preallocate app.S1 (i think this might cause an error, because appdesigner does not want you to append things to app?), but then you overwrite app.S1 inside your loop
5. You preallocate array1 and never use it