Merci M. laurent - les adjonctions sont perfect!

***

While the MINVERSE.EXT worked for my application (I was unable to invert beyond 51x51), the function is limited to 256 columns in width (the natural limit of the sheet obviously) and so, 256 rows in depth as well.

If you really need to invert larger forms, one could always try partitioning the larger matrix into smaller sub-matrices.

See this link for a "quick and dirty" review of inverting partitioned matrices:

http://www.cc.utah.edu/~nahaj/math/matrix.inverse.notes.html
Note:

A is m x m,

B is m x n,

C is n x m, and

D is n x n

only the A and D partitions need be inverted and are presumeably of managable size.

****

Here's another question though... When will Excel expand beyond the current 256 column limitation? It seems to me that today's computers could handle much more than that (say Column ZZ ---> 676 columns) even if we had to sacrifice some of the thousands of rows that I only use rarely.