convmtx (Communications Toolbox)

Convolution matrix of Galois field vector

Syntax

```
A = convmtx(c,n);
```

Description

A convolution matrix is a matrix, formed from a vector, whose inner product with another vector is the convolution of the two vectors.

A = convmtx(c,n) returns a convolution matrix for the Galois vector c. The output A is a Galois array that represents convolution with c in the sense that conv(c,x) equals

A*x, if c is a column vector and x is any Galois column vector of length n. In this case, A has n columns and m+n-1 rows.
x*A, if c is a row vector and x is any Galois row vector of length n. In this case, A has n rows and m+n-1 columns.

Examples

The code below illustrates the equivalence between using the conv function and multiplying by the output of convmtx.

m = 4;
c = gf([1; 9; 3],m); % Column vector
n = 6;
x = gf(randint(n,1,2^m),m);
ck1 = isequal(conv(c,x), convmtx(c,n)*x) % True
ck2 = isequal(conv(c',x'),x'*convmtx(c',n)) % True

The output is

```
ck1 =

     1


ck2 =

     1
```

See Also

conv

convenc cosets