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## Re: type 3 sums of squares

**From**: |
John Darrington |

**Subject**: |
Re: type 3 sums of squares |

**Date**: |
Sat, 1 Jan 2011 14:03:06 +0000 |

**User-agent**: |
Mutt/1.5.18 (2008-05-17) |

If I understand correctly, the sums of squares is not a single scalar.
Instead we require a value for each factor. So the result needs to be an
array or a matrix.
I was envisaging a function with a signature similar to
void type3ssq (gsl_matrix *cov, const struct categoricals *x);
which would mutate cov, placing the ssqs in elements of the matrix.
Note that "struct categoricals" contains both "vars" and "n_vars".
GLM will, at some stage, require to support interactions. I think there
is a relatively straightforward extention to "struct categoricals" which
will make it support interactions. So if GLM can be implemented in terms
of it, that will make our lives a lot easier later.
To answer your specific question, I suggest that the function lives outside
of glm.c since there are a number of other potential commands which perform
similar function.
J'
On Fri, Dec 31, 2010 at 05:01:12PM -0500, Jason Stover wrote:
I am getting around to coding type 3 sums of squares. I think
the easiest approach is to put a function in linreg.c whose call
would be something like
ssq = linreg_type3_ssq (cov, vars, n_vars, l);
Where l is a linreg struct, and the other args are what they seem to
be.
My question is: Should this be something in glm.c, so as to avoid use
of linreg.c by glm.c? Or should glm.c depend on linreg.c?
I think using linreg.c would hide a lot details about computation of
type 3 sums of squares. On the other hand, it would necessitate
creating a linreg struct. But then again, having a linreg struct may
be useful if PSPP ever gets to a point where one procedure can use
data structures from previously called procedures.
-Jason
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