Plotting and calculating difference

Jw
2012 1 13
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I have 2 matrix containing data of timestamps, 1 X Nth matrix I loaded them into the workspace and i want to plot the data on x axis and in the same figure. their size of matrix are different.
load('observations.mat');
load('control-times.mat');
index=880;
timestamp = ctrl_times(:,index:end);
obser_time = observation_times(:,1:end);
fig=figure;
hold on; axis equal;
plot(timestamp(1,:),'b*');
After plotting, how do i calculate the difference between data of the 2 matrices?
For example 1st data of timestamp - 1318496774.36108
however obser_time data starts from column 140 - 1318496774.90708
I would require looping if i am not wrong.
Thanks in advance.

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Walter Roberson
Walter Roberson 2012-1-13
If the two matrices are 1 x N, N different between the two, then why does your code show them being accessed with a range index for both the first and second indices ? (:,index:end) and (:,1:end) are both syntaxes that suggest strongly that 2D matrices are being used.
Jw
Jw 2012-1-13
In actual case, for my control-times,it originally has 1x11827 matrix however i only wanted to use the 880 column onwards and till the end of the control-times matrix
yes they are 2D matrices.
Walter Roberson
Walter Roberson 2012-1-13
Is your ctrl_times a row vector, or is it a matrix for which size(ctrl_times,1) is greater than 1 ? If it is a row vector, why do you confuse things by indexing it with : as its first element?
If they are row vectors as you appear to indicate, then clearer code would be
timestamp = ctrl_times(index:end);
obser_time = observation_times;
Jw
Jw 2012-1-13
oh ok my mistake of indexing it with :
Walter Roberson
Walter Roberson 2012-1-13
Okay, so now please expand on what you mean by obser_time data starts from column 140 ? Do you mean the first 139 columns are NaN, or do you mean that column 1 of obser_time logically corresponds to column 140 of timestamp ?
Jw
Jw 2012-1-13
basically what i need to do is plot the timestamp and obser_time and compare them. 1st to 139th values of obser_time are zeros.
I need to compare the both data. If there is a obser_time data that occurs before the next timestamp, find the difference in the time between the obser_time data and the previous timestamp.

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Walter Roberson
Walter Roberson 2012-1-13

0 个投票

Hours to find out what you really wanted to do. Less than a minute to solve once that was known.
plot(timestamp, 'b*', obser_time, 'r+'); %your plot
padtimestamp = [0 timestamp inf];
[counts, binnums] = histc(obser_time, padtimestamp);
timestampdiff = obser_time - padtimestamp(binnums); %compared

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Jw
Jw 2012-1-15
encounter this error while debugging. I suppose its because my timestamp is 1x10948 and my obser_time is 1x2072.
??? Error using ==> plot
Not enough input arguments.
Error in ==> timeintervals at 9
plot(timestamp, 'b*', obser_time, 'r+'); %your plot
Walter Roberson
Walter Roberson 2012-1-16
plot(1:length(timestep), timestamp, 'b*', 1:length(obser_time), obser_time, 'r+'); %your plot
Jw
Jw 2012-1-17
Now that i have gotten the difference between the obser_time to the previous timestamp, is it possible to also get the difference between the obser_time to the next timestamp??
Walter Roberson
Walter Roberson 2012-1-17
nextdiff = padtimestamp(binnums+1) - obser_time;
Note if there is an observ_time which is exactly the same or greater than the largest timestamp, then this nextdiff time will be infinity.

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