MATLAB: How to add the first row all the odd columns by step of 2 odd columns

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I want to add 1 and 3 the 2 and 1. Then moving to second row I want to add 1 and 1 then 4 and 5. Similarly I want to, in general, using using loop for an image
a = [...    
       1     2     3     1
       1     4     1     5
       5     8     5     9
       1     9     2     1]

Best Answer

Try this:
a1=a(:,1:2:end) %for odd columns 
a2=a(:,2:2:end) %for even columns
oddcolumns=sum(a1,2)
evencolumns=sum(a2,2)
a
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