Growing array with fscanf data in matlab

I am trying to send a value to an arduino from Matlab and read serial data with fscanf() in matlab from the arduino.

My requirements are that i need to be able to send the data at a specified time interval i.e 20 values persecond at .05 seconds. and i need to be able to graph the incoming data and be able to save it for later use. I will know the length of the array before I start I have read and seen that this can be used to speed up the process.

The problem i am currently having is that each iteration of the loop becomes successively longer which throws the time behavior off more. I believe this to be due to the growing array inside of the loop I have.

    delete(instrfindall);
clear all; clc; close all;
oldserial1 = instrfind ('Port', 'COM8'); 
if (~isempty(oldserial1))
 disp('COM8 is in use; deleting now');
 delete(oldserial1)
end
handles.UltraM=serial('COM8', 'BaudRate', 115200,'Timeout',10000000);
handles.UltraM.InputBufferSize= 10^6;
handles.UltraM.OutputBufferSize= 10^6;
fopen(handles.UltraM);
max = 80;
min = 40;
amp = (max-min)/2;
offset = amp + min;
btime = 5;
bpm = 12;
spb = 60/bpm;
sapb = spb/.05;
tosd = sapb*bpm*btime;
time1 = btime*60;
x = linspace(0,time1,tosd)';
x1 = amp*sin(x*(2*pi/20)) + offset;
y = zeros(length(x),1);
i = 1;
figure(1);
hold on;
title('Pressure Data');
xlabel('Data Number');
ylabel('Analog Voltage (0-1023)');
t1 = zeros(length(x),1);
figure(2);
hold on;
title('Time to execute task');
xlabel('iteration number');
ylabel('time taken');
while (i<=length(x))
    t2 = tic;
    t = tic;
    fprintf(handles.UltraM,(['<P' num2str(x1(i)) '>']));
    disp((['<P' num2str(x1(i)) '>']));
    y(i) = fscanf(handles.UltraM,'%i');
    figure(1);
    hold on;
    plot(i, y(i), 'b*');
    plot(i, pressure, 'b*');
    drawnow;
    hold off;
 while toc(t) < 0.05
     continue
 end
    t1 = toc(t2);
    figure(2);
    hold on; 
    plot(i,t1,'b*');
    drawnow;
    hold off;
    i = i + 1; 
end

The last tic toc finction is just used so that i can graphically see the slowdown time.

thank you in advance for any help

[dpb]

"...each iteration of the loop becomes successively longer ...[and]... I believe this to be due to the growing array inside of the loop"

x = linspace(0,time1,tosd)';
...
y = zeros(length(x),1);
...
while (i<=length(x))
  t2 = tic;
  t = tic;
  fprintf(handles.UltraM,(['<P' num2str(x1(i)) '>']));
  disp((['<P' num2str(x1(i)) '>']));
  y(i) = fscanf(handles.UltraM,'%i');
  ...

You have preallocated y; I don't see which array you think is "growing" inside the loop?

I wonder if the slowdown isn't more due to adding more datapoints to the plot instead...see what happens if you just comment out all the stuff updating the plot and only read the data just to confirm/deny and determine what is (or, just as importantly, isn't) the bottleneck. Gotta' be sure you're attacking the right problem, first.

[Ethan Gardner]

I actually tested that out awhile back and found that it was a problem with the plot i still need to be able to plot but i need to do it in a more efficent manner. the code i have for the plot now looks like this:

if true
  % code
clear all;
max = 80;
min = 40;
amp = (max-min)/2;
offset = amp + min;
btime = 2;
bpm = 12;
spb = 60/bpm;
sapb = spb/.05;
tosd = sapb*bpm*btime;
time1 = btime*60;
x = linspace(0,time1,tosd)';
x1 = amp*sin(x*(2*pi/20)) + offset;
figure(1);
hold on;
title('Incomming Data from External Device');
xlabel('Data Number');
ylabel('Analog Voltage (0-1023)');
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
% while loop & Timing Data
i = 1;
y = zeros(length(x),1);
t2 = tic;
while i<=length(x)
  t = tic;
  disp(['<P' num2str(x1(i)) '>']);
  y = sin(i);
  r = rem(i,100);
  figure(1);
  if i<=100
      xlim([0 i]);
      ylim([-1 1]);
      d = (1:i);
  else 
      xlim([i-100 i]);
      ylim([-1 1]);
      d = (i-100:i);
  end
%     if r == 0
%         clf(figure(1),'reset');
%     end
  plot(i,y,'b*');
  drawnow;
while toc(t) < 0.05
  continue
end
  i = i+1;
end
t3 = toc(t2);
disp(t3);
%t3 = 166 seconds expect ~120
end

so i am now trying to figure out how to make this still plot in real time but still be fast i only need x amount of data points to be shown at one time. this runs faster but still not optimally as if i was just plotting one point on the graph is it possible to speed it up.

[dpb]

See the section in the doc on "Animation" under the 2D/3D Plots subject for detailed discussion; for this type the use of simply redefining the [X|YData] properties and updating appropriately instead of using the high-level calls...

Answer 1

[Ethan Gardner]

figured it out this works perfectly for my applicaiton

if true
  clear all;
max = 80;
min = 40;
amp = (max-min)/2;
offset = amp + min;
btime = 2;
bpm = 12;
spb = 60/bpm;
sapb = spb/.05;
tosd = sapb*bpm*btime;
time1 = btime*60;
x = linspace(0,time1,tosd)';
x1 = amp*sin(x*(2*pi/20)) + offset;
figure(1);
hold on;
title('Incomming Data from External Device');
xlabel('Data Number');
ylabel('Analog Voltage (0-1023)');
figure(2);
hold on;
title('Incomming Data from External Device');
xlabel('Data Number');
ylabel('Analog Voltage (0-1023)');
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
% while loop & Timing Data
i = 1;
y = zeros(length(x),1);
t2 = tic;
while i<=length(x)
  t = tic;
  disp(['<P' num2str(x1(i)) '>']);
  y(i) = sin(i);
  r = rem(i,100);
  figure(1);
  if i<=100
      xlim([0 i]);
      %ylim([-1 1]);
      d = (1:i);
  else 
      xlim([i-100 i]);
      %ylim([-1 1]);
      d = (i-100:i);
  end
    if isinteger(int64(r)) == true
        clf(figure(1),'reset');
    end
  plot(d,y(d),'b*');
  drawnow;
while toc(t) < 0.05
  continue
end
% figure(2);
% plot(i,y(i),'b*');
  i = i+1;
end
t3 = toc(t2);
disp(t3);
% d =1:length(x);
% figure(1);
% plot(x,y,'b*');
%t3 = 166 seconds expect ~120
end