My customer has the following situation to set up a DOE:
3 components of a mixture (S, X, M, could be treated as mixture or continous) plus a filler component (W), as well two suppliers for each of the ingredients S and X, called OS and OX (each categorical with two levels).
The difficulties raise with the constraints, first the ranges:
Range S 0 -0.04
Range X 0-0.006
Range M 0-0.07
Range W 0.884-1
OS L1, L2
OX L1, L2
Or as continuous, where the range expresses the percentage and the filler is not necessary anymore as they are not interested at all in the effect of the filler itself
Range S 0 -4 [%]
Range X 0-0.6 [%]
Range M 0-7 [%]
OS L1, L2
OX L1, L2
In addition there are the following requirements:
- S+X >0, so that S and X cannot be 0 at the same time
- If X==0, S must be >0.5% (but if X!=0, S can be 0)
- If S ==0, X must be >0.05% (but if S!=0, X can be 0)
- If S==0, OS is not allowed/makes no sense
- If X==0, OX is not allowed/makes no sense
The issue is that there cannot be constraints with the mixture factors other than the ranges or a simple linear constraint to ensure S+X>0. And in the continuous case we could not manage to set the constraints in a way to fulfill all constraints. Not with linear ones, nor with disallowed combinations, and a mixture of both is not possible either.
Any ideas how I could create a design with the above settings?
Attached some things I tried so far. In one I have created a design close to the requirements but thought it’s not balanced enough as there is no run where S or X alone occurs. Please see the three scripts to illustrate the behaviours, and especial the one with the 3 level categorical, as there are multiple designs included. Factors are saved in tables to your convenience
Thanks for your support,
Martin