Vector calculus identities
The following identities are important in vector calculus:
Gradient of a tensor field, , of order n, is generally written as
and is a tensor field of order n + 1. In particular, if the tensor field has order 0 (i.e. a scalar), , the resulting gradient,
is a vector field.
The divergence of a tensor field, , of non-zero order n, is generally written as
and is a contraction to a tensor field of order n − 1. Specifically, the divergence of a vector is a scalar. The divergence of a higher order tensor field may be found by decomposing the tensor field into a sum of outer products, thereby allowing the use of the identity,
where is the directional derivative in the direction of multiplied by its magnitude. Specifically, for the outer product of two vectors,
For a 3-dimensional vector field , curl is generally written as:
and is also a 3-dimensional vector field.
For a tensor field, , the laplacian is generally written as:
and is a tensor field of the same order.
In Feynman subscript notation,
where overdots define the scope of the vector derivative. The dotted vector, in this case B, is differentiated, while the (undotted) A is held constant.
For the remainder of this article, Feynman subscript notation will be used where appropriate.
Product rule for the gradient
Product of a scalar and a vector
Vector dot product
Alternatively, using Feynman subscript notation,
As a special case, when A = B,
Vector cross product
Curl of the gradient
Divergence of the curl
Divergence of the gradient
The Laplacian of a scalar field is defined as the divergence of the gradient:
Note that the result is a scalar quantity.
Curl of the curl
Here,∇2 is the vector Laplacian operating on the vector field A.
Summary of important identities
Addition and multiplication
Below, the curly symbol ∂ means "boundary of".
In the following curve–surface integral theorems, S denotes a 2d open surface with a corresponding 1d boundary C = ∂S (a closed curve):
Notes and references
- Feynman, R. P.; Leighton, R. B.; Sands, M. (1964). The Feynman Lecture on Physics. Addison-Wesley. Vol II, p. 27–4. ISBN 0-8053-9049-9.
- Kholmetskii, A. L.; Missevitch, O. V. (2005). "The Faraday induction law in relativity theory". arXiv:physics/0504223 [physics.class-ph].
- Doran, C.; Lasenby, A. (2003). Geometric algebra for physicists. Cambridge University Press. p. 169. ISBN 978-0-521-71595-9.
- Balanis, Constantine A. Advanced Engineering Electromagnetics. ISBN 0-471-62194-3.
- Schey, H. M. (1997). Div Grad Curl and all that: An informal text on vector calculus. W. W. Norton & Company. ISBN 0-393-96997-5.
- Griffiths, David J. (1999). Introduction to Electrodynamics. Prentice Hall. ISBN 0-13-805326-X.