Change X axis units

Hi!

I was given some data where Y axis is in uV and X axis in seconds. I want to change both units to mV and to hours.

My problem is that the data is "loaded" to my matlab code, for instance:

s1=load('data.txt');

So I don't know how to change the units.

Answer 1

[Ameer Hamza]

In the following example, I assumed that 1st column in data.txt is x-values and 2nd column is y-values

s1 = load('data.txt');
t = s1(:,1);
uV = s1(:,2);

t_hour = t/3600;
mV = uV/1000;

plot(t_hour, mV)

[Laura Ferrer Pascual]

Thank you, but I must have specified my question.

After loading the data, I have functions defined by this data, for instance:

RE=interp1(s1(:,1), s1(:,2), t, 'nearest');

TE=interp1(s2(:,1), s2(:,2), t, 'nearest')

And then I define another function, for example O=RE-TE

So I don't want to plot(t_hour,mV), I want to plot(O). So is it possible to change the units after defining TE and RE?

[Ameer Hamza]

interp1() is a piecewise linear transformation, so you can change the units after calculating RE and TE too.

RE=interp1(s1(:,1), s1(:,2), t, 'nearest');
TE=interp1(s2(:,1), s2(:,2), t, 'nearest');
O=RE-TE;
O_mV = O/1000;
plot(t/3600, O_mV)

[Laura Ferrer Pascual]

Sorry I think I'm not explaining very well. s1 has two columns (one for x values and another for y values), so RE and TE are functions that depend on x and y (uV and s), and therfore the function 0 also depends on x and y, is not just y

[Ameer Hamza]

From your code, if I understand correctly, RE and TE have units of seconds (y-values) and variable 't' have unit of 'uV'. Are you trying to do this, or the units are opposite?

[Laura Ferrer Pascual]

Is the opposite, RE and TE have units of uV and t of seconds

[Ameer Hamza]

But what about units of columns in data.txt. Is first (seconds) and second (uV)?

[Laura Ferrer Pascual]

Yes! First column is s and second column is uV

[Ameer Hamza]

In that case, the unit of RE and TE are also uV. Consequently, the unit of O is also uV. The last code in my comment should work.

Answer 2

[KSSV]

To convert seconds to hours multiply t by

t_in_hours = t_in_seconds*1/(60*60) ; 

To convert uV to mV, multiply v by

V_in_mV = V_in_uV*1/1000 ; 

[Steven Lord]

To make the time conversion a bit more self-explanatory in the code you can use the seconds and hours functions.

>> s = 7200;
>> h = hours(seconds(s))
h =
     2

Another example: a million minutes is a little under 2 years.

>> years(minutes(1e6))
ans =
          1.90132431040869

There's also a days function you can use for this purpose.