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{{For|generator matrices in probability theory|transition rate matrix}} | |||
In [[coding theory]], a '''generator matrix''' is a [[Basis (linear algebra)|basis]] for a [[linear code]], generating all its possible codewords. | |||
If the matrix is ''G'' and the linear code is ''C'', | |||
:''w'' = '''c'''G | |||
where ''w'' is a [[codeword]] of the linear code ''C'', '''c''' is a row vector, and a [[bijection]] exists between ''w'' and '''c'''. A generator matrix for an (<math>n</math>, <math>M = q^k</math>, <math>d</math>)<sub><math>q</math></sub>-code has dimensions ''k''×''n''. Here ''n'' is the length of a codeword, ''k'' is the number of information bits, ''d'' is the minimum distance of the code, and ''q'' is the number of symbols in the alphabet (thus, ''q'' = 2 indicates a [[binary code]], etc.). The number of [[Redundancy (information theory)|redundant bits]] is denoted by ''r = n - k''. | |||
The [[Systematic code|systematic]] form for a generator matrix is | |||
: <math>G = \begin{bmatrix} I_k | P \end{bmatrix}</math> | |||
where <math>I_k</math> is a ''k''×''k'' [[identity matrix]] and P is of dimension ''k''×''r''. | |||
A generator matrix can be used to construct the [[parity check matrix]] for a code (and vice-versa). | |||
==Equivalent Codes== | |||
Codes C<sub>1</sub> and C<sub>2</sub> are equivalent (denoted C<sub>1</sub> ~ C<sub>2</sub>) if one code can be created from the other via the following two transformations: | |||
# permute components, and | |||
# scale components. | |||
Equivalent codes have the same distance. | |||
The generator matrices of equivalent codes can be obtained from one another via the following transformations: | |||
# permute rows | |||
# scale rows | |||
# add rows | |||
# permute columns, and | |||
# scale columns. | |||
==See also== | |||
* [[Hamming code (7,4)]] | |||
==External links== | |||
* [http://mathworld.wolfram.com/GeneratorMatrix.html MathWorld entry] | |||
{{DEFAULTSORT:Generator Matrix}} | |||
[[Category:Coding theory]] | |||
Latest revision as of 10:02, 27 February 2013
28 year-old Painting Investments Worker Truman from Regina, usually spends time with pastimes for instance interior design, property developers in new launch ec Singapore and writing. Last month just traveled to City of the Renaissance. In coding theory, a generator matrix is a basis for a linear code, generating all its possible codewords. If the matrix is G and the linear code is C,
- w = cG
where w is a codeword of the linear code C, c is a row vector, and a bijection exists between w and c. A generator matrix for an (, , )-code has dimensions k×n. Here n is the length of a codeword, k is the number of information bits, d is the minimum distance of the code, and q is the number of symbols in the alphabet (thus, q = 2 indicates a binary code, etc.). The number of redundant bits is denoted by r = n - k.
The systematic form for a generator matrix is
where is a k×k identity matrix and P is of dimension k×r.
A generator matrix can be used to construct the parity check matrix for a code (and vice-versa).
Equivalent Codes
Codes C1 and C2 are equivalent (denoted C1 ~ C2) if one code can be created from the other via the following two transformations:
- permute components, and
- scale components.
Equivalent codes have the same distance.
The generator matrices of equivalent codes can be obtained from one another via the following transformations:
- permute rows
- scale rows
- add rows
- permute columns, and
- scale columns.