Affine Geometry (redirected from Affine-geometric)

affine geometry: see geometry.

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affine geometry [ə′fīn jē′äm·ə·trē]

(mathematics)

The study of geometry using the methods of linear algebra.

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Affine Geometry 

a branch of geometry that studies those properties of figures in a plane or in space that are preserved under any affine transformation of the plane or space. An example of such a transformation is the transformation of similitude. The properties of a geometric figure which are preserved under any affine transformation are naturally called the affine invariants of this figure. A basic affine invariant is the simple ratio of three points M₁, M₂, and M₃ which lie on a straight line. If x₁x₂, and x₃ are the respective abscissas of these points, then the simple ratio is equal to (x₂ − x₁) / (x₃ − x₂). The affine invariants of any system consisting of n points (n ≥ 4) can be expressed in terms of simple ratios. Hence, in particular, it follows that the center of gravity of a geometric figure is preserved in affine transformations. In arbitrary affine transformations, parallel straight lines remain parallel. The methods and facts of affine geometry are widely used in different branches of natural science—mechanics, theoretical physics, and astronomy. For example, small deformations of a continuous medium, elastic in the first approximation, can be studied by the methods of affine geometry.

REFERENCES

Aleksandrov, P. S. Lektsii po analiticheskoi geometrii. Moscow, 1968.
Efimov, N. V. Vysshaia geometriia, 4th ed. Moscow, 1961.

E. G. POZNIAK