DCTRANS  discrete cosine transform
Usage:
DCTRANS x dir n
Inputs:
x

input vector

dir

direction: 'Forward ' or 'Inverse '

n

the number of coefficients

Outputs:
y

vector containing result of transformation

Function:
Discrete Cosine Transform (DCT)  forward and inverse. The DCT is defined as follows:
for , for
The forward DCT is defined by the formula:
If dir is Forward
:
if 0 < n < len(x)

only the first n coefficients are stored in the output

otherwise

len(x) coefficients are stored in the output

The definition of the inverse discrete cosine transform is:
If dir = Inverse
:
if 0 < n < len(x)

only the first n coefficients of x are used for the


inverse transformation (the others are set to 0 );


transformation and output length = len(x)

if n > len(x)

vector x is expanded with zeros to length n


transformation and output length = n

otherwise

transformation and output length = len(x)
