OF matrix
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Matrix of O-Factors (or OF matrix) is a matrix of optimum factors in SuperMemo (starting with version 5 in 1989). The matrix is indexed by item difficulty (expressed as E-factor or A-factor), and by stability (expressed as repetition number or repetition number category).
In Algorithm SM-17, the role of the 2-dimensional OF matrix is played by the 3-dimensional stability increase matrix (SInc[]) with an added dimension of retrievability.
This glossary entry is used to explain "History of spaced repetition" by Piotr Wozniak (June 2018)