/* PSPP - a program for statistical analysis.
Copyright (C) 2007 Free Software Foundation, Inc.
This program is free software: you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation, either version 3 of the License, or
(at your option) any later version.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program. If not, see . */
/*
An interaction is a gsl_vector containing a "product" of other
variables. The variables can be either categorical or numeric.
If the variables are all numeric, the interaction is just the
scalar product. If any of the variables are categorical, their
product is a vector containing 0's in all but one entry. This entry
is found by combining the vectors corresponding to the variables'
OBS_VALS member. If there are K categorical variables, each with
N_1, N_2, ..., N_K categories, then the interaction will have
N_1 * N_2 * N_3 *...* N_K - 1 entries.
When using these functions, make sure the orders of variables and
values match when appropriate.
*/
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