Hi @Byron_JMP,

I also thought about using Mixture design, but since the total quantity of X1+X2+X3+X4 is not fixed (it should be between 9 and 18 units), I switched to an Optimal factorial design.

The Mixture design can be a good alternative for this use case by adding a 5th continuous factor for the total quantity of component that can vary between 9 and 18 :

Specifying a Scheffé Cubic model and adding a quadratic effect for X5 (Total Quantity) enables to have an interesting design respecting all the constraints :

(Value of X4 for row25 could be switched to 0 without big changes, to avoid using 4 components in the mixture if really needed).

Script to generate the design :

```
DOE(
Custom Design,
{Add Response( Maximize, "Y", ., ., . ), Add Factor( Mixture, 0, 0.89, "X1", 0 ),
Add Factor( Mixture, 0, 0.89, "X2", 0 ), Add Factor( Mixture, 0, 0.89, "X3", 0 ),
Add Factor( Mixture, 0, 0.22, "X4", 0 ),
Add Factor( Continuous, 9, 18, "Total Quantity", 0 ),
Set Random Seed( 1320459420 ), Number of Starts( 743 ), Add Term( {1, 1} ),
Add Term( {2, 1} ), Add Term( {3, 1} ), Add Term( {4, 1} ), Add Term( {5, 1} ),
Add Term( {1, 1}, {2, 1} ), Add Term( {1, 1}, {3, 1} ),
Add Term( {1, 1}, {4, 1} ), Add Term( {2, 1}, {3, 1} ),
Add Term( {2, 1}, {4, 1} ), Add Term( {3, 1}, {4, 1} ),
Add Term( {1, 1}, {2, 1}, {3, 1} ), Add Term( {1, 1}, {2, 1}, {4, 1} ),
Add Term( {1, 1}, {3, 1}, {4, 1} ), Add Term( {2, 1}, {3, 1}, {4, 1} ),
Add Term( {1, 1}, {2, 1} ), Add Term( {1, 1}, {3, 1} ),
Add Term( {2, 1}, {3, 1} ), Add Term( {1, 1}, {4, 1} ),
Add Term( {2, 1}, {4, 1} ), Add Term( {3, 1}, {4, 1} ), Add Term( {5, 2} ),
Add Alias Term( {1, 1}, {5, 1} ), Add Alias Term( {2, 1}, {5, 1} ),
Add Alias Term( {3, 1}, {5, 1} ), Add Alias Term( {4, 1}, {5, 1} ),
Set Sample Size( 30 ), Simulate Responses( 0 ), Save X Matrix( 0 ), Make Design}
)
```

And datatable is attached.

Hope this discussion may help @stat_ranger,

Victor GUILLER

Scientific Expertise Engineer

L'Oréal - Data & Analytics