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  2. Geometry index - Wikipedia

    en.wikipedia.org/wiki/Geometry_index

    where: α and β are the two greatest valence angles of coordination center; θ = cos −1 (− 1 ⁄ 3) ≈ 109.5° is a tetrahedral angle. When τ 4 is close to 0 the geometry is similar to square planar, while if τ 4 is close to 1 then the geometry is similar to tetrahedral.

  3. Index of a subgroup - Wikipedia

    en.wikipedia.org/wiki/Index_of_a_subgroup

    A subgroup H of finite index in a group G (finite or infinite) always contains a normal subgroup N (of G), also of finite index. In fact, if H has index n, then the index of N will be some divisor of n! and a multiple of n; indeed, N can be taken to be the kernel of the natural homomorphism from G to the permutation group of the left (or right ...

  4. Intersection (set theory) - Wikipedia

    en.wikipedia.org/wiki/Intersection_(set_theory)

    Intersections of the unaccented modern Greek, Latin, and Cyrillic scripts, considering only the shapes of the letters and ignoring their pronunciation Example of an intersection with sets. The intersection of two sets and , denoted by , [3] is the set of all objects that are members of both the sets and .

  5. Voronoi diagram - Wikipedia

    en.wikipedia.org/wiki/Voronoi_diagram

    Let be a metric space with distance function .Let be a set of indices and let () be a tuple (indexed collection) of nonempty subsets (the sites) in the space .The Voronoi cell, or Voronoi region, , associated with the site is the set of all points in whose distance to is not greater than their distance to the other sites , where is any index different from .

  6. Projections onto convex sets - Wikipedia

    en.wikipedia.org/wiki/Projections_onto_convex_sets

    In mathematics, projections onto convex sets (POCS), sometimes known as the alternating projection method, is a method to find a point in the intersection of two closed convex sets. It is a very simple algorithm and has been rediscovered many times. [1] The simplest case, when the sets are affine spaces, was analyzed by John von Neumann.

  7. Cartesian product - Wikipedia

    en.wikipedia.org/wiki/Cartesian_product

    An important special case is when the index set is , the natural numbers: this Cartesian product is the set of all infinite sequences with the i-th term in its corresponding set X i. For example, each element of ∏ n = 1 ∞ R = R × R × ⋯ {\displaystyle \prod _{n=1}^{\infty }\mathbb {R} =\mathbb {R} \times \mathbb {R} \times \cdots } can ...

  8. Set theory - Wikipedia

    en.wikipedia.org/wiki/Set_theory

    Since sets are objects, the membership relation can relate sets as well, i.e., sets themselves can be members of other sets. A derived binary relation between two sets is the subset relation, also called set inclusion. If all the members of set A are also members of set B, then A is a subset of B, denoted A ⊆ B.

  9. Codimension - Wikipedia

    en.wikipedia.org/wiki/Codimension

    the two sets of constraints may not be compatible. The first of these is often expressed as the principle of counting constraints : if we have a number N of parameters to adjust (i.e. we have N degrees of freedom ), and a constraint means we have to 'consume' a parameter to satisfy it, then the codimension of the solution set is at most the ...