Don't "double-up" cell indexing; makes dereferencing much more complicated than need be...
Define x as
x{1,1}=[0.8,1.4];
x{1,2}= [2.6,2,3.4];
x{1,3}= [1,2];
instead. Then it's simply
>> cellfun(@sum,x)
ans =
2.2000 8.0000 3.0000
>>
If there is some reason (but I can't think of what that could be) that the "cell inside a cell" simply must be, then you've got to do a bit more work...
x{1,1}={0.8,1.4};
x{1,2}= {2.6,2,3.4};
x{1,3}= {1,2};
>> cellfun(@(x) sum([x{:}]),x)
ans =
2.2000 8.0000 3.0000
>>
Remembering to use them and having to write all those extra brackets and curlies is a lot of complexity; just "don't do that!" by nesting and avoid it.
