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MathGroup Archive 2006

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one-dimensional and two-dimensional convolution

  • To: mathgroup at smc.vnet.net
  • Subject: [mg69076] one-dimensional and two-dimensional convolution
  • From: "bd satish" <bdsatish at gmail.com>
  • Date: Tue, 29 Aug 2006 04:47:36 -0400 (EDT)
  • Sender: owner-wri-mathgroup at wolfram.com

Hi buddies ,

    Here is the definition of a 1-dimensional discrete-time convolution
(encountered in Signals & Systems ,etc)  of two functions x[n] and
h[n] :

 y[n] = Sum[ x[k] * h[n-k] , { k , -Infiniy , Infinity }]

 The above command works when x[n] and y[n] are functions in the strict
sense (say , x[n] = Exp[-2*pi*n/6] UnitStep[n] and h[n] = Exp[-4*Pi*n/7]
UnitStep[n] )
 But in Signal processing , we often have lists :

 X= { 1,2,3,1,-1 }  , H = { 1,-4,5,6} etc.  where the entries are the
function's values at different values of n .  i.e.

 X =  {  x[0] , x[1] , x[2] , x[3] , x[4] } . Similarly   H = { h[0] , h[1]
, h[2] , ... }   (, say )

  Without using Sum ( and DiscreteDelta ) , is there any way to directly (&
quickly) find the convolution sum.
I'm finding convolution of lists whose lengths are typically 700 to 1000. So
the code needs be really fast.

The Mathematica command  " ListConvolve "  did not help me. Anybody plz help
me out !!

     Also ,  the 2-dimensional convolution of     two-variable functions ,
f[x,y] and h[x,y]  is defined as :

 z[x,y] = Sum[ Sum[ f[m,n]  * h[x-m , y-n] , { m , -Infinity, Infinity } ] ,
{ n , -Infinity , Infinity } ]

 But in image processing  , we often have nested lists. In this case ,
f[x,y] and h[x,y] are matrices :

 f = { { 1,2,3 } , { 4,5,6 } ,{7,8,9} } etc. Similarly  h . There are no
restrictions on the dimensions of matrices f and h .

 Mathgroup , plz help me in  solving these 1-D and 2-D convolutions !!



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