How can I get the result of, e.g., poly(1:3. degree=2) to give me the
unnormalized integer coefficients
usually used to explain orthogonal polynomial contrasts, e.g,
-1 1
0 -2
1 1
As I understand things, the columns of x^{1:degree} are first centered
and then
are normalized by 1/sqrt(col sum of squares), but I can't
see how to relate this to what is returned by poly().
> poly(1:3, degree=2)
1 2
[1,] -7.071068e-01 0.4082483
[2,] -9.073264e-17 -0.8164966
[3,] 7.071068e-01 0.4082483
attr(,"degree")
[1] 1 2
attr(,"coefs")
attr(,"coefs")$alpha
[1] 2 2
attr(,"coefs")$norm2
[1] 1.0000000 3.0000000 2.0000000 0.6666667
attr(,"class")
[1] "poly" "matrix"
>
I've read the code for poly(), but $alpha and $norm2 are undocumented,
and I still still can't see the inverse
transformation
-Michael
--
Michael Friendly Email: friendly AT yorku DOT ca
Professor, Psychology Dept.
York University Voice: 416 736-5115 x66249 Fax: 416 736-5814
4700 Keele Street http://www.math.yorku.ca/SCS/friendly.html
Toronto, ONT M3J 1P3 CANADA
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