how to plot substracted data

if true

   function test(data,t)
figure;
fprintf(1,'%s %d\n', t, length(data));
plot((data(2:end,2)-data(1:end-1,2))./1000000000,data(:,3),'r-');
hold on;
plot((data(2:end,2)-data(1:end-1,2))./1000000000,data(:,4),'g-');
plot((data(2:end,2)-data(1:end-1,2))./1000000000,data(:,5),'b-');
title(t);
dt = (data(2:end, 2)- data(1:end-1, 2))./1000000000;
figure;
hist (dt, [0:0.002:0.5]);
title(t);

end

hi all, i try to subtract the values as shown above so that i can get the time in seconds(the 2nd column in the data contains timestamps in nanoseconds) as shown below:

1 144274932861 -0.16280572 9.49301 -0.36391866

2 144279571533 0.10295067 9.557653 -0.46926352

3 144284942626 0.2908955 9.586384 -0.5650316

4 144289581298 0.2837129 9.657013 -0.51595044

5 144294952392 0.09816227 9.685743 -0.46088383

6 144299591064 -0.09696517 9.736021 -0.33638534

7 144304962158 -0.19871874 9.750386 -0.32680854

8 144309631347 -0.12090719 9.783905 -0.40940848

9 144314971923 0.075417355 9.828198 -0.47524905

10 144319610595 0.14963761 9.831789 -0.46447513 etc

so at the end of the day i want to get the timestamp(2nd column) in secs.

However, the error message that i get is: Matrix dimensions must agree.

Error in test (line 5) plot(data(2:end,2)-data(1:end,2),data(:,3),'r-');

any idea? thanks!

Answer 1

[Andrew]

So from what I see it looks like you are trying to simply subtract one timestamp from the previous 1. In that case all you need to do is

plot([0;data(2:end,2)-data(1:end-1,2)],data(:,3),'r-');

Also, It's not a good idea to use true as a variable because it's a key word in matlab for a logical true.

EDIT: I realized you would have a mismatch in size between the two vectors so you need to add a 0 at the beginning. This makes sense because your first measurement should happen at time 0

[Daniel Barzegar]

well, i did what you are saying, but the plot doesnt seem to be giving the "right" result

[Andrew]

what do you expect to see/what exactly are you trying to do?

[Daniel Barzegar]

i basically want to make the time values in the x axis start from 0 and also convert them into sec. I attach you a file that you can use as the data, to check it .

[Andrew]

Ok, I figured out what you are trying to do. What you actually want to do is this:

plot(data(1:end,2)-data(1,2),data(:,3),'r-')

What you were doing before was plotting the time between each step

[Andrew]

If you have an old version of MATLAB you may need:

plot(data(1:end,2)-data(1,2)*ones(size(data(1:end,2))),data(:,3),'r-')

[Daniel Barzegar]

yes, that's it! thanks :)