convol

Arguments

h

a vector, first input sequence ("short" one)

x

a vector, second input sequence ( "long" one)

e0

a vector,old tail to overlap add (not used in first call)

y

a vector, the convolution.

e1

new tail to overlap add (not used in last call)

Description

Calculates the convolution y= h*x of two discrete sequences by using the fft. The convolution is defined as follows:

Overlap add method can be used.

USE OF OVERLAP ADD METHOD: For x = [x1, x2,..., xNm1, xN] First call is [y1, e1] = convol(h, x1); Subsequent calls : [yk, ek] = convol(h, xk, ekm1); Final call : [yN] = convol(h, xN, eNm1); Finally y = [y1, y2,..., yNm1, yN].

The algorithm based on the convolution definition is implemented for polynomial product: y = convol(h, x) is equivalent to y = coeff(poly(h,'z','c') * poly(x,'z','c')) but much more efficient if x is a "long" array.

Examples

x = 1:3;
h1 = [1,0,0,0,0];
h2 = [0,1,0,0,0];
h3 = [0,0,1,0,0];
x1 = convol(h1, x)
x2 = convol(h2, x)
x3 = convol(h3, x)
convol(h1+h2+h3, x)
p1 = poly(x,'x','coeff')
p2 = poly(h1+h2+h3, 'x', 'coeff')
p1 * p2

See also

• corr — correlation, covariance
• fft — Transformée de Fourier discrète directe ou inverse uni-, bi-, ou N-dimensionnelle
• pspect — two sided cross-spectral estimate between 2 discrete time signals using the Welch's average periodogram method.