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An equivalent formulation in this context is the following: [4] A congruence relation on an algebra A is a subset of the direct product A × A that is both an equivalence relation on A and a subalgebra of A × A. The kernel of a homomorphism is always a congruence. Indeed, every congruence arises as a kernel.
In mathematics, two square matrices A and B over a field are called congruent if there exists an invertible matrix P over the same field such that P T AP = B. where "T" denotes the matrix transpose. Matrix congruence is an equivalence relation.
In elementary geometry the word congruent is often used as follows. [2] The word equal is often used in place of congruent for these objects. Two line segments are congruent if they have the same length. Two angles are congruent if they have the same measure. Two circles are congruent if they have the same diameter.
For example, in modular arithmetic, for every integer m greater than 1, the congruence modulo m is an equivalence relation on the integers, for which two integers a and b are equivalent—in this case, one says congruent—if m divides ; this is denoted ().
This is equivalent to saying that one triangle (or its mirror image) is an enlargement of the other. Any two pairs of sides are proportional, and the angles included between these sides are congruent: [6]
In mathematics, an isometry (or congruence, or congruent transformation) is a distance-preserving transformation between metric spaces, usually assumed to be bijective. [ a ] The word isometry is derived from the Ancient Greek : ἴσος isos meaning "equal", and μέτρον metron meaning "measure".
Thus an equivalence relation over , a partition of , and a projection whose domain is , are three equivalent ways of specifying the same thing. The intersection of any collection of equivalence relations over X (binary relations viewed as a subset of X × X {\displaystyle X\times X} ) is also an equivalence relation.
In the definition of similarity, if the matrix P can be chosen to be a permutation matrix then A and B are permutation-similar; if P can be chosen to be a unitary matrix then A and B are unitarily equivalent. The spectral theorem says that every normal matrix is unitarily equivalent to some diagonal matrix.