cputime and tic...toc: high time difference

cputime and tic...toc are giving very different execution times. I am doing:

function[time, output2] = foo(input1, input2)
    start = cputime;
    tic;
    ...some computation
    toc
    tic;
    ...some computation
    toc
    ...eccetera
    tic;
    ...some computation
    toc
    time = cputime - start;
end

and I get this:

[t, ~] = foo(input1, input2)

Elapsed time is 0.564095 seconds.
Elapsed time is 119.898174 seconds.
Elapsed time is 76.127796 seconds.
Elapsed time is 3.465138 seconds.
Elapsed time is 0.240975 seconds.

t =

  376.4200

that doesn't sum up to the total time at all. Why is it that? There are no code lines exluded between tic...tocs

Answer 1

[Steven Lord]

See the "The cputime Function vs. tic/toc and timeit" section on this documentation page. One potential big difference is how many threads are working and for how much of the time they're working versus sitting idle waiting for something to do.