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0 pointseigenket2y ago0 comments

I feel like matrix multiplication/linear maps are kinda the "wrong" things to be considering when you're talking about applying them to lines or shapes in euclidean space.

For example there is no linear map which maps a line (or segment) through the origin to a parallel line (or segment of the same length) that doesn't pass through the origin, even though these are clearly just the same object shifted around a bit.

A much more natural set of operations is (IMO) the affine transformations since then I can move things around as you expect. I find dealing with linear maps of lines or circles or polygons a bit unintuitive.

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4 comments · 2 top-level

whiterknight2y ago· 2 in thread

Affine transforms for N dimensions can be represented as matrices/linear maps in dimension N+1

eigenketOP2y ago

Sure, but that isn't what they're doing on that webpage. They're just directly applying linear maps to shapes in R^2.

You can represent a wild variety of things by linear maps on suitably enlarged spaces.

whiterknight2y ago

Agreed. Context: This sub thread is discussing how to interpret matrices as an abstract thing that does something as opposed to the mechanics of multiplying

ReleaseCandidat2y ago

> For example there is no linear map which maps a line (or segment) through the origin to a parallel line (or segment of the same length) that doesn't pass through the origin, even though these are clearly just the same object shifted around a bit.

That's why god (well, projective geometrists) made homogeneous coordinates. Without them geometry isn't much fun when using linear algebra (as you have way too many special cases).

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