Sum of subsets /= sum of whole??

I have a MATfile (attached) containing a 3-dimensional array of size [90 144 120]. The array is called ba_lm3. If I subset the array into two equally-sized halves, the sum of all values in each of those halves is different from if I sum all values in the original array. Take a look:

>> sum(ba_lm3(:))
ans =
    46601836
>> sum(sum(sum(ba_lm3(:,73:144,:)))) + sum(sum(sum(ba_lm3(:,1:72,:))))
ans =
    46604364

The 2nd (subsetted) dimension of the sub-arrays is indeed 72+72=144:

>> size(ba_lm3(:,73:144,:))
ans =
    90    72   120
>> size(ba_lm3(:,1:72,:))
ans =
    90    72   120
>> size(ba_lm3)
ans =
    90   144   120

And I don't think there should be any overlap.

I have observed this problem on machines running MATLAB r2009b and r2013b, so I think it must either be a problem with my code or the array. Any ideas?

[pietro]

I cannot open the attached .mat file: it is not reconignized from my matlab.

[Azzi Abdelmalek]

Your problem is not clear

[James Tursa]

What is the class of ba_lm3?

Answer 1

[Azzi Abdelmalek]

a_lm3 is a single array, if you want to get the same result

ba_lm3=double(ba_lm3);
a=ba_lm3(:,1:72,:);
b=ba_lm3(:,73:144,:);
s1=sum(ba_lm3(:))
s2=sum(a(:))+sum(b(:))

[Sam]

That's it! Thanks so much.