Time on X-axis

I'm and trying to plot real time data in MatLab and I am having trouble determining how to go about putting time on the x-axis. I tried working with 'datenum', but it seems like to use this you would need a predetermined time.

For example I want to see something like 7:30:25 for each tick..

Can this function be used? Would a different function work better to continually update and plot real time?

Thank you

Answer 1

[Wayne King]

After calling plot() with datenum()

use datetick

datetick('x','HH:MM:SS')

For example:

    x = linspace(now, now+1, 12*6+1);
    % Create a sample plot
    plot(x, (1:length(x)).^2);
    datetick('x', 'HH:MM PM')

[Steve]

Thanks for the quick response Wayne.

But this gives a time of "12:00:00 AM" across the entire axis. I need the plot to show the current time (or as close as possible) of when the point is recorded.

I apologize if this is something simple. I am still somewhat new to MatLab.

[Wayne King]

can you give a simple example of your time vector, say 10-20 elements of it and the data. So we can do an example

[Steve]

Maybe I am confused. I don't have a time vector. I was using the example you had illustrated above...I want to plot real time data, so I'm not sure what to put within datenum(). The MatLab help shows a predetermined date.

Answer 2

[Steve]

Well I thought I found an answer, but I guess I didn't. I tried using 'clock' which produces a 6 element array that starts with year and ends with seconds. This is what I tried:

c=clock
Time = [(int2str(c(4)) ':' int2str(c(5)) ':' int2str(c(6)))]

In the MatLab command window, it works great. It produced a something like 17:13:34 which is exactly what I want. However, when I try to plot this I get an error:

Unexpected MATLAB expression.

Are there any options for plotting time with data that is contiuously updating?

[Walter Roberson]

Time = sprintf('%02d:%02d:%02d', c(4), c(5), c(6));

What do you get in the command window if you execute

datestr(linspace(now, now+1, 12*6+1),'HH:MM PM')

Answer 3

[Steve]

Time = sprintf('%02d:%02d:%02d', c(4), c(5), c(6));

Thanks Walter, this is what I am looking for. However when I try to use this to plot, I get the following error:

??? Error using ==> plot
Invalid first data argument

Error in ==> GRAPH at 10
        plot(Time,Out1)

This is what my code looks like:

count = 0;
Out1 = nan(1, 30);
while count < 3
    for i = 1 : 30
        num1 = rand + 1; 
        c=clock;
        Out1 = [Out1(2:end), num1];
        Time = sprintf('%02d:%02d:%02f', c(4), c(5), c(6));
        plot(Time,Out1)
        pause(0.1);
    end
    count = count + 1;
end

[KRUNAL]

I have date in column 1 and time in column 2 and data in column three. I want to plot date/time against that data. Can anyone tell me how can I do it?