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Alan Beban[_2_] Alan Beban[_2_] is offline
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Default solving a matrix in Excel

Dare wrote:

The augmented matrix

AA1 AB1 AC1 ... AH1 | AI1
AA2 AB2 AC2 ... AH2 | AI2
AA3 AB3 AC3 ... AH3 | AI3
.
.
AA8 AB8 AC8 ... AH8 | AI8

I attempted to solve with the two operations,

=MINVERSE(AA1:AH8) saved in AA11:AH18
=MMULT(AA11:AH18,AI1:AI8)

in Excel, but all I got was garbage. Some ove the cells were very
large (1E14). When I tediously solved the matrix using elementary row
operations, there was virtually no error. Did I do something wrong?

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The methodology is correct; the solution vector should be given by

=MMULT(MINVERSE(AA1:AH8),AI1:AI8)

Perhaps you'd like to post the elements of the constituent matrices so
we can reproduce your problem. Excel is not always very good at
extracting the inverse when some of the results are very large or very
small.

Alan Beban