Rather than trying to use the SUM function, would either of these functions
work for what your trying to do (it was a little unclear to me, and it's been
awhile since I've used matrices regularly)

MINVERSE, MDETERM, MMULT

These were the first few hits I got when doing a XL help file search for
"matrix".

--
Best Regards,

Luke M
*Remember to click "yes" if this post helped you!*


"Aale de Winkel" wrote:

Using Excel in magic square research I created a lot of rather complicated
matrix statements doing simple things, summing a skew line I need to pick
each cell seperately. I thought using sum with a fairly simple matrix
function would save a lot of work attempts like
SUM(index(A1:F6;row()-row(a1)+(rowcel)+1;column()-column(a1)+(colcel)+1))
(discarding the function (rowcel) and (colcel) for this post which are
stements using the target row / column)
failed me, sum seems not to be matrix function capable, nor can I find a sum
version that would do the trick (is there any(?)) could matrix cabability be
added in future Excel.
Small matrices aren't a problem if course but for magic squares of higher
order using matrix functions within sum() would save a lot of work copying
and pasting.