Darren Hill wrote...
....
So, for example, assume input column B and output column C, here's the
steps I'd need to do:
B2 * sum (C3:c11) +
B3 * sum (C4:c11) +
B4 * sum (C5:c11) +
B5 * sum (C6:c11) +
B6 * sum (C7:c11) +
B7 * sum (C8:c11) +
B8 * sum (C9:c11) +
B9 * sum (C10:c11) +
B10 * sum (C11:c11)
....

Use the array formula

=SUM(B2:B10*MMULT(--(ROW(C3:C11)<=TRANSPOSE(ROW(C3:C11))),C3:C11))