polar coordinates
Let be Cartesian coordinates for .
Then , related to by
are the polar coordinates for . It is simply written .
The polar coordinates of Cartesian coordinates are
where is defined here (http://planetmath.org/OperatornamearcTanWithTwoArguments).
Polar basis.Polar coordinates are equipped with an orthonormal base , which can be defined in terms of the standard cartesian base in as follows.
where are so-called radial and traverse or angular vector, respectively. Since these vectors are variable in direction, they are differentiable. In fact,
The geometrical action of the derivative operator is like a rotation operator that rotates each base vector a counter-clockwise angle equals to .
Position vector. For an arbitrary point of polar coordinates , its position vector comes given by the single equation
Relations with complex numbers.When the Euclidean plane
is identified with by
it is possible to define multiplications on . Via polar coordinates, the formula for this multiplication becomes very simple, thanks to Euler’s formula (http://planetmath.org/EulerRelation)
Thus, we have the following identification:
If and , the product of and works out to be.(Even if one is not familiar with the complex exponential
, this assertion may be checkeddirectly using the angle sum identities for and .)
Multiplications of polar coordinates have some simple geometricinterpretations. For example, if and ,then given by is the rotation
of byangle . If , then canbe viewed as the scaling
of along the ray by . Note also that multiplication by has the same effectas multiplication by the scalar .
For more on polar coordinates, including their construction and extensions on domain of polar coordinates and , see here (http://planetmath.org/ConstructionOfPolarCoordinates).
Calculus in polar coordiantes.For reference, here are some formulae for computing integrals and derivativesin polar coordinates. The Jacobian for transforming from rectangular topolar cordinates is
so we may compute the integral of a scalar field as
Partial derivative operators transform as follows: