How to give multi stimulation simultaneously?

I want to give stim1 and stim2 simultaneously, but I can only see the latter one on oscilloscope even though the monkeylogic screen shows that stim1 and stim2 are both given. How to make both stim1 and stim2 output simultaneously and successfully? Thank you!


Here is the relative code:

% y = repmat([5 0 5 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0]', 4000, 1);
% fs = 5000;
% save('stim_waveform.mat','y','fs');

stim1 = Stimulator(null_);
stim1.Channel = 1;
stim1.Waveform = 'stim_waveform.mat';

stim2 = Stimulator(null_);
stim2.Channel = 2;
stim2.Waveform = [5,0,0,0,0]';
stim2.Frequency = 1000;

stim = Concurrent(stim1);
stim.add(stim2);

tc = TimeCounter(stim);
tc.Duration = 20000;
scene = create_scene(tc);
run_scene(scene, scene_start);

Use one Stimulator only. Assign [1 2] to Channel. Waveform should be a n-by-2 matrix. Please read the manual carefully.
https://monkeylogic.nimh.nih.gov/docs_RuntimeFunctions.html#Stimulator