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what are the differences between affine and vector spaces ?

Please can you give me examples.

thanks

roger

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- Thread starter roger
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- #1

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what are the differences between affine and vector spaces ?

Please can you give me examples.

thanks

roger

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matt grime

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http://mathworld.wolfram.com/AffineSpace.html

an example wolud be a straight line (not necessarily through the origin). if you like it is a vector subspace that has been shifted in some direction

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HallsofIvy

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For example, in R

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mathwonk

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a nice way to compare the two is this i think: imagine a flat affine space, everywhere homogeneous but no origin or coordinates. then consider the family of all translations of this space. those form a vector space of the same dimension, and the zero translation is the origin.

given any point of the affine space, any translation takes it to another point such that those two ordered points form a vector that determines the translation. vice versa, given two ordered points of affine space, i.e. a vector, there is a unique translation taking the foot of the vector to the head.

so there is a natural way to construct an associated vector space from an affine space, such that the vector space acts on the affine space by translation.

and if we fix any one point of affine space, i.e. an "origin", then this sets up a 1-1 correspondence between points of the affine space and elements of the vector space.

so this is a special case of a group acting on a set, and here the action is fre and transitive, so the set is a homogeneous space for the group.

given any point of the affine space, any translation takes it to another point such that those two ordered points form a vector that determines the translation. vice versa, given two ordered points of affine space, i.e. a vector, there is a unique translation taking the foot of the vector to the head.

so there is a natural way to construct an associated vector space from an affine space, such that the vector space acts on the affine space by translation.

and if we fix any one point of affine space, i.e. an "origin", then this sets up a 1-1 correspondence between points of the affine space and elements of the vector space.

so this is a special case of a group acting on a set, and here the action is fre and transitive, so the set is a homogeneous space for the group.

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