Sum the deltas of my matrix
Python 2, 42 bytes



lambda m:sum(r[-1]-r[0]for r in m+zip(*m))


An unnamed function taking a list of lists, m, and returning the resulting number.

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How?

The sum of the deltas of a list is the last element minus the first, everything else just cancels:
(r[n]-r[n-1])+(r[n-1]-r[n-2])+...+(r[2]-r[1]) = r[n]-r[1]

The zip(*m) uses unpacking (*) of m to pass the rows of m as separate arguments to zip (interleave) and hence transposes the matrix. In python 2 this yields a list (of tuples, but that's fine), so we can add  (concatenate) it to (with) m, step through all our rows and columns, r, perform the above trick for each and just add up the results (sum(...)).