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Re:Less Weird Quaternions Using Geometric Algebra by defen on Monday August 07, 2017 @03:54PM (#14950708)
A bivector is a plane spanned by two vectors, with an associated orientation.
Re:Less Weird Quaternions Using Geometric Algebra by abainbridge on Monday August 07, 2017 @03:58PM (#14950744)
That hasn't helped!
Re:Less Weird Quaternions Using Geometric Algebra by klodolph on Monday August 07, 2017 @06:05PM (#14951650)
Think in terms of magnitude (which can be positive or negative) and direction.

Think of a scalar. It has a magnitude but it doesn't have a direction. It's 0-dimensional.

Think of a vector. It has a magnitude (the size of the vector) and it also has a direction, which points in a straight line through the origin. It's 1-dimensional. For example, the vector (2,0,0) has magnitude 2 and points along the X-axis. You could write that as 2 * x, if x is the vector (1,0,0).

A bivector also has a magnitude, but instead of being 0-dimensional (like a scalar) or 1-dimensional (like a vector, it's 2-dimensional. So you could have a bivector that "points" along the entire XY-plane (remember: two-dimensional) and has some magnitude, say, 5. You could write that as 5 * x * y, if x is (1,0,0) and y is (0,1,0).

If you attach physical units to these things, then you might have units of meters for vectors, and square meters for bivectors.

Having an understanding of subspaces in linear algebra is helpful.

Re:Less Weird Quaternions Using Geometric Algebra by defen on Monday August 07, 2017 @04:10PM (#14950851)
In a geometric setting - if you have two vectors, you can position them so that both have one end at the origin. This spans a plane (test it out yourself in 2D or 3D space with two pencils, put the eraser at the origin for each; it's a parallelogram). The area of the plane will depend on the length of the pencils. You can assign an orientation to the plane by imagining a rotor embedded in the plane that spins either clockwise or counterclockwise.
Re:Less Weird Quaternions Using Geometric Algebra by abainbridge on Tuesday August 08, 2017 @03:18AM (#14955273)
Hmmm.

"The area of the plane will depend on the length of the pencils". Surely the area of the plane is infinite? The area of the _parallelogram_ will depend on the length of the pencils.

And I can't see how "you can assign an orientation to the plane" other than by changing the directions of the pencils. Again this description sounds like it refers to the parallelogram, not the plane.

And I don't know what a rotor is.

But other than that, I'm doing great.

Re:Less Weird Quaternions Using Geometric Algebra by defen on Tuesday August 08, 2017 @03:15PM (#14961475)
Yes, when I said plane I really meant the parallelogram. By rotor I literally just meant "a thing that spins" - you could draw a circle on the parallelogram with an embedded arrow describing the direction it is spinning - that arrow could either be going clockwise or counterclockwise.
Re:Less Weird Quaternions Using Geometric Algebra by klodolph on Tuesday August 08, 2017 @09:02AM (#14957342)
The length of a line is infinite too. If you think of a vector as a line + magnitude, it's a bit more natural to think of a bivector as a plane + magnitude.
Re:Less Weird Quaternions Using Geometric Algebra by Govindae on Tuesday August 08, 2017 @10:38AM (#14958164)
Do you know what a vector is? Vector:Line == Bivector:Plane

A vector is an oriented (+,-) magnitude(length) _in_ a line. A Bivector is an oriented (+,-) magnitude(area) _in_ a plane.

That area does not have any particular shape.