The linearity conditions required by LP solver are not satisfied

Hi All! This is my first post on the site, please inform me if I've done anything wrong.

I am using the Simplex LP solver to maximise a function, subject to a few constraints.

The solver will return the maximum solution for some input constants, however, if I change the constant to some values the error "The linearity conditions required by LP solver are not satisfied" will appear.

I am confused by this as I am not changing any equations or constraints, just the value of the input.

I have attached the excel file. Maximum production rate is being maximised, subject to material, labour and machine constraints. If cell C32 is changed from 1 to 0.9 (meaning that labour is constraining the maximum production rate) the error will appear. If cell C36 is changed from 5 to 5.1 the error will appear.

Any advice would be greatly appreciated. Thanks.

Hi
Solver can not handle the restriction H18<=F32.

When you change C32 to 0.9 people needed grows to 55,556 witch is higher than its restriction 'ppl Labor = 50000'

Thanks for your reply.

Yes, though if you change all the yellow boxes such that the constraint is met (with the value at 0.9), then run the solver, the same error appears. I don't see why the solver works for 1 but doesn't work for 0.9 under these conditions.

I tried several experiments, because if it worked for MV = 1 should also work for other values (linearity).
But the problem you expose is not linear. Whether the total number of people required and the total machines are non-linear functions.
Try to see if C32 = 0.9, H15: H17 = 0 and I15: I17 = 0, the solver returns the optimal solution to the problem (the total ppl is linear =G14/C32).
Keep the value of C32 = 1 and modify the Labour efficiency HV from 2 to 0.9 and you will have a problem with linearity of the total machines needed.
Solution?
Try to construct a solution that put restriction for each 'Site Type'/'Gride Type' and not for the total people or total machinery

Thanks again for your reply.

I actually just figured out the problem. It was to do with the roundup function in the labour and machine calculation. For some reason this messed up with the linearity under certain conditions.

Thank you so much for your help. Much appreciated.

You are welcomed.