Change of Coordinate Systems
From Math Images
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As can be easily verified. | As can be easily verified. | ||
- | Often useful is mapping points from '''Cartesian Coordinates''' to '''[[Polar Coordinates]]'''. Such a mapping, as shown in this page's main image, can map a disk to a rectangle. Each origin-centered ring in the disk consists of points at constant distance from the origin and angles ranging from 0 to <math> 2\pi </math>. These points create a vertical line in Polar Coordinates. Each ring at different distance from the origin creates its own line in the polar system, and the collection of lines creates a rectangle. | + | The ellipse that is tilted relative to the coordinate axes is created by a combination of rotation and stretching, represented by the matrix |
+ | : <math>\begin{bmatrix} | ||
+ | |||
+ | 2cos(\theta) & -sin(\theta)\\ | ||
+ | 2sin(\theta) & cos(\theta) \\ | ||
+ | \end{bmatrix}\vec{x} = \vec{x'}</math> | ||
+ | |||
+ | Often useful is mapping points from '''Cartesian Coordinates''' to '''[[Polar Coordinates]]'''. Such a mapping, as shown in this page's main image, can map a disk to a rectangle. Each origin-centered ring in the disk consists of points at constant distance from the origin and angles ranging from 0 to <math> 2\pi </math>. These points create a vertical line in Polar Coordinates. Each ring at a different distance from the origin creates its own line in the polar system, and the collection of lines creates a rectangle. | ||
Revision as of 14:48, 11 June 2009
Change of Coordinates |
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Change of Coordinates
- The same object, here a circle, can look completely different depending on which coordinate system is used.
Basic Description
It is a common practice in mathematics to use different coordinate systems to solve different problems. An example of a switch between coordinate systems follows: suppose we take a set of points in regular x-y Cartesian Coordinates, represented by ordered pairs such as (1,2), then multiply their x-components by two, meaning (1,2) in the old coordinates is matched with (2,2) in the new coordinates.Under this transformation, a set of points would become stretched in the horizontal x-direction since each point becomes further from the vertical y-axis (except for points originally on the y-axis, which remain on the axis). A set of points that was originally contained in a circle in the old coordinates would be contained by a stretched-out ellipse in the new coordinate system, as shown in this page's main image.
Many other such transformations exist and are useful throughout mathematics, such as mapping the points in a disk to a rectangle.
A More Mathematical Explanation
Some of these mappings can be neatly represented in matrix notation, in the form
UNIQ299616b459c1e [...]Some of these mappings can be neatly represented in matrix notation, in the form
Where is the coordinate vector of our point in the original coordinate system and is the coordinate vector of our point in the new coordinate system.
For example the transformation in the basic description, doubling the value of the x-coordinate, is represented in this notation by
As can be easily verified.
The ellipse that is tilted relative to the coordinate axes is created by a combination of rotation and stretching, represented by the matrix
Often useful is mapping points from Cartesian Coordinates to Polar Coordinates. Such a mapping, as shown in this page's main image, can map a disk to a rectangle. Each origin-centered ring in the disk consists of points at constant distance from the origin and angles ranging from 0 to . These points create a vertical line in Polar Coordinates. Each ring at a different distance from the origin creates its own line in the polar system, and the collection of lines creates a rectangle.
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