Error in the plot function/low resolution

Hi everyone!

I have an EMG signal at 1000Hz. When I use the plot(EMG signal), the x values only move at 10 ms (anything inside this gets the same x value), the y values are working fine (upper pic). If I cut the signal to a smaller piece, the error is gone (lower pic). I need the 1ms resolution to define events.

Answer 1

[Pedro Valadao]

Hi all,

It is not an error. It is just the precision of the datatip function. It is easily adjustable on the following line:

formattedValue = [valueFormat num2str(value,4) removeValueFormat];

i found this info on the following discussion:

https://www.mathworks.com/matlabcentral/answers/288287-how-to-increase-the-range-of-measurement-of-data-cursor-in-a-plot

Cheers!

Pedro.

Answer 2

[Maximilian Schönau]

Hi, it is hard to find (and fully understand) your problem without having your code.

If I understand your question right, you want to be your upper plot in a better resolution. Since you have the data probably available in a better resolution (second plot), I would guess that some function deletes some values on the way, it could be for example the function linspace(x1,x2,resolution) which does this to your data.

Answer 3

[Pedro Valadao]

Hi Max,

Thank you for the quick reply! The same error occurs with the following code:

v = rand(1,150000),plot(v) % here the error happens as in the upper figure
figure, plot v(1:200) % here the error does not happen as in the lower figure

I have checked multiple files with the same type of data, .mlx and .m - the same problem happens consistently.

Br, P.

[Maximilian Schönau]

That should not be the case. As far as i know, MATLAB does not shorten your data you plot in a visible way, which often causes speed problems because people plot more data than they should do.

If I run the code you sent I cannot see any difference in the resolution. When I zoom in the right plot the displayed data is the same as in the left plot

[Maximilian Schönau]

Maybe some different MATLAB IDE causes that? Do you juse the appdesigner, a life skript or MATLAB online?

[Pedro Valadao]

Hi, I'm using matlab R2020a installed on my pc.

v = rand(1,150000)
figure, subplot(2,1,1), plot(v), subplot(2,1,2), plot(v(1:200))

If I zoom both a lot and use the data tips, the following happens:

[Pedro Valadao]

Hi @Star Strider,

sorry if this is too much of a newby question, I'm tagging you because you have answered pretty much all questions I have seen in this forum! haha

Could you please help?

Br, Pedro.