Why do I need to divide by 12 in the second line to make it equal to line 1?

year_avg = mean(sum(sum(sum(dl,1),2),3),4);  
year_avg= mean(sum(dl(:)))/12;

[Paolo]

What is dl ?

[Nesha Wright]

Oh sorry!

dl = total(:,:,:,i:i+11); %data for one year over all dimemsions,

"total" is a 4D emissions file

[Basil C.]

If I'm not wrong you don't need to use mean because the output of

(sum(sum(sum(dl,1),2),3),4) and

sum(dl(:))

is a single number and not a vector.

[Nesha Wright]

If I remove the mean, I get a 4-D single array, however, I am still not sure what the difference between my first two lines in the original question is (regarding the 12).

Answer 1

[Image Analyst]

dl is a 4-D array. Think of it as a 3-D volumetric chunk of data, and there are 12 of them, like 12 blocks.

Now, what exactly do you want to do with those 12 blocks?

Average each block so that you have 12 averages - an average over all elements in each block?

Or an average over all possible elements over all 12 blocks so that you have only one average? If so, try this:

year_avg = mean(dl(:));

[Image Analyst]

So I take it that this solved your question (because you accepted it)? So is that question you have in the comment above still a question?

[Nesha Wright]

Your response helps, however, the results of

 year_avg = mean(dl(:));

is not equal to either of these so I am still not sure what the difference between these two specific lines is:

year_avg = mean(sum(sum(sum(dl,1),2),3),4);

year_avg= mean(sum(dl(:)))/12;

[Image Analyst]

Please answer my questions. Do you expect 1 number, or 12 numbers?

[Nesha Wright]

1 number. Thanks.

[Image Analyst]

 year_avg = mean(dl(:));

should work. It will give you a single number that is the mean of all the values in that 3-D array. Attach your data in a .mat file so I can find out what's wrong.

[Nesha Wright]

The file is too large to attach, it is monthly emissions data for multiple years, dimensions are lat, long, sector (where the emissions are from) and time (monthly). Because the time is monthly that is why in line 2 I divide by 12 however I am not sure why I don't need to do so in line 1.

[Image Analyst]

And you can't read it in and save just a few years worth of data in a new .mat file??? OK, whatever. Failing having some data to work with all I can say is that the code should work.