- Correlation (projective geometry)
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This article is about correlation in projective geometry. For other uses, see correlation (disambiguation).
A correlation is a duality (collineation from a projective space onto its dual space, taking points to hyperplanes (and vice versa) and preserving incidence) from a projective space to itself. In the case of projective planes correlations can only exist if the plane is self-dual.
If a correlation σ is involutory (that is, two applications of the correlation equals the identity: σ²(P)=P for all points P) then it is called a polarity.
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