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ffdesign2()

Usage:
 ```ffdesign2(basis), integer matrix basis containing confounding generators ```

Keywords: design, aliasing, factorial
```ffdesign2(basis) finds the set of factor/level combinations used in the
2^(k-p) fractional factorial corresponding to the given generators.  The
result is a CHARACTER vector giving the factor/level combinations.

The p x k matrix basis contains the generators for the aliasing, one row
for each generator and one column for each factor in the design.  The
elements in basis are 0, -1, or 1.  A nonzero entry indicates that a
factor is present in the generator for that row. The sign of a generator
is the product of the signs of the nonzero elements of the generator.
For example, 1 0 1 0 0 -1 means -ACF is a generator (alias of I).

Examples:
Cmd> print(b, format:"2.0f") # Matrix b is 2x5, so 2^(5-2) design
b:
(1,1)  1  1  1  0  0      [ABC is a generator]
(2,1)  0  0  1  1 -1      [-CDE is a generator]

Cmd> ffdesign2(b)
(1) "ce"
(2) "a"
(3) "b"
(4) "abce"
(5) "dc"