Solver Constraints

[twa14]

I use a land survey spreadsheet which uses solver to minimise the contents of
a cell subject to the contents of three other cells being reduced to zero.
The content of these three cells are set to zero in the constraints menu of
solver. During the solve procedure only 2 cells reduce to zero. The errant
cell holds its original value. the cell is not protected in any way. If I add
the constraint for this cell twice to the constraints menu (thus 4
constraints instead of the necessary 3, 2 of which are the same) the cell
does reduce to zero during the solve procedure???. It does not however give
the correct answer, close but not acceptable. The problem itself is solvable
as I have done so using two other different methods. Only solver is spoiling
my day

 

[Bernard Liengme]

Send me the file and I will have a look
best wishes

 

[twa14]

Thanks for the reply, I came across the problem at work where we use Excel
2000 (Dutch). I have now tried the problem on my home PC using Excel 2002
(USA) and it does solve the problem. All three constraints reduce to zero. I
decided to try again at work but got the same results. I carry the
spreadsheet on a USB stick so there is no question of different versions of
the same problem. On both computers, adding the same constraint twice or
more does give different solutions. I had not expected this behaviour, my
understanding of solver is probably defective. I will send you on the
spreadsheet with some notes. It still gives the wrong answer on both PC's