同余关系和等价关系有什么区别?


回答 1:

大卫·乔伊斯(David Joyce)的回答很好,但是我见过关于同余关系的另一种定义(亨格福德的代数):

令G为具有等价关系〜的单面体。

〜是全等关系,如果

fora,b,c,din[math]G[/math],if[math]a[/math] [math]b[/math]and[math]c[/math] [math]d[/math]then[math]ac[/math] [math]bd.[/math]for a, b, c, d in [math]G[/math], if [math]a [/math]~[math] b[/math] and [math] c [/math]~[math] d[/math] then [math]ac [/math]~[math] bd.[/math]

Thisisusefultodefinenormalsubgroups,andquotientgroupsbecauseG/ isagroupwithabinaryoperationthatrespectsthecongruencerelation.This is useful to define normal subgroups, and quotient groups because G/~ is a group with a binary operation that respects the congruence relation.


回答 2:

Therearetworelationsknownascongruencerelations.Oneisingeometryandreferstocongruentfigures.Twofiguresarecongruentifthereisarigidmotionthatmovesonetotheother.Theotherisinnumbertheoryandreferstointegerscongruentmodulonwhere[math]n[/math]issomefixedinteger.Twointegersarecongruentmodulo[math]n[/math]iftheirdifferenceisdivisibleby[math]n.[/math]Thissecondcongruencerelationhasbeenextendedtoelementsofaringmoduloanideal.There are two relations known as congruence relations. One is in geometry and refers to congruent figures. Two figures are congruent if there is a rigid motion that moves one to the other. The other is in number theory and refers to integers congruent modulo n where [math]n[/math] is some fixed integer. Two integers are congruent modulo [math]n[/math] if their difference is divisible by [math]n.[/math] This second congruence relation has been extended to elements of a ring modulo an ideal.

两者都是等价关系。可能还有其他等价关系,称为等价关系。

对于您的问题的答案,同余关系是一种特殊的等价关系,后来被称为同余关系。