Metric Spaces¶
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class
sage.categories.metric_spaces.MetricSpaces(category, *args)¶ Bases:
sage.categories.metric_spaces.MetricSpacesCategoryThe category of metric spaces.
A metric on a set \(S\) is a function \(d : S \times S \to \RR\) such that:
- \(d(a, b) \geq 0\),
- \(d(a, b) = 0\) if and only if \(a = b\).
A metric space is a set \(S\) with a distinguished metric.
Implementation
Objects in this category must implement either a
diston the parent or the elements ormetricon the parent; otherwise this will cause an infinite recursion.Todo
- Implement a general geodesics class.
- Implement a category for metric additive groups and move the generic distance \(d(a, b) = |a - b|\) there.
- Incorporate the length of a geodesic as part of the default distance cycle.
EXAMPLES:
sage: from sage.categories.metric_spaces import MetricSpaces sage: C = MetricSpaces() sage: C Category of metric spaces sage: TestSuite(C).run()
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class
Complete(base_category)¶ Bases:
sage.categories.category_with_axiom.CategoryWithAxiomThe category of complete metric spaces.
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class
ElementMethods¶ -
abs()¶ Return the absolute value of
self.EXAMPLES:
sage: CC(I).abs() 1.00000000000000
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dist(b)¶ Return the distance between
selfandother.EXAMPLES:
sage: UHP = HyperbolicPlane().UHP() sage: p1 = UHP.get_point(5 + 7*I) sage: p2 = UHP.get_point(1 + I) sage: p1.dist(p2) arccosh(33/7)
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class
ParentMethods¶ -
dist(a, b)¶ Return the distance between
aandbinself.EXAMPLES:
sage: UHP = HyperbolicPlane().UHP() sage: p1 = UHP.get_point(5 + 7*I) sage: p2 = UHP.get_point(1.0 + I) sage: UHP.dist(p1, p2) 2.23230104635820 sage: PD = HyperbolicPlane().PD() sage: PD.dist(PD.get_point(0), PD.get_point(I/2)) arccosh(5/3)
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metric()¶ Return the metric of
self.EXAMPLES:
sage: UHP = HyperbolicPlane().UHP() sage: m = UHP.metric() sage: p1 = UHP.get_point(5 + 7*I) sage: p2 = UHP.get_point(1.0 + I) sage: m(p1, p2) 2.23230104635820
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class
SubcategoryMethods¶ -
Complete()¶ Return the full subcategory of the complete objects of
self.EXAMPLES:
sage: Sets().Metric().Complete() Category of complete metric spaces
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class
WithRealizations(category, *args)¶ Bases:
sage.categories.with_realizations.WithRealizationsCategory
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class
sage.categories.metric_spaces.MetricSpacesCategory(category, *args)¶ Bases:
sage.categories.covariant_functorial_construction.RegressiveCovariantConstructionCategory-
classmethod
default_super_categories(category)¶ Return the default super categories of
category.Metric().Mathematical meaning: if \(A\) is a metric space in the category \(C\), then \(A\) is also a topological space.
INPUT:
cls– the classMetricSpacescategory– a category \(Cat\)
OUTPUT:
A (join) category
In practice, this returns
category.Metric(), joined together with the result of the methodRegressiveCovariantConstructionCategory.default_super_categories()(that is the join ofcategoryandcat.Metric()for eachcatin the super categories ofcategory).EXAMPLES:
Consider
category=Groups(). Then, a group \(G\) with a metric is simultaneously a topological group by itself, and a metric space:sage: Groups().Metric().super_categories() [Category of topological groups, Category of metric spaces]
This resulted from the following call:
sage: sage.categories.metric_spaces.MetricSpacesCategory.default_super_categories(Groups()) Join of Category of topological groups and Category of metric spaces
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classmethod