Section: Signal Processing Functions
conv2 function performs a two-dimensional convolution of
matrix arguments.  The syntax for its use is
    Z = conv2(X,Y)
which performs the full 2-D convolution of X and Y.  If the 
input matrices are of size [xm,xn] and [ym,yn] respectively,
then the output is of size [xm+ym-1,xn+yn-1].  Another form is
    Z = conv2(hcol,hrow,X)
where hcol and hrow are vectors.  In this form, conv2
first convolves Y along the columns with hcol, and then 
convolves Y along the rows with hrow.  This is equivalent
to conv2(hcol(:)*hrow(:)',Y).
You can also provide an optional shape argument to conv2
via either
    Z = conv2(X,Y,'shape')
    Z = conv2(hcol,hrow,X,'shape')
where shape is one of the following strings
'full' - compute the full convolution result - this is the default if no shape argument is provided.
 'same' - returns the central part of the result that is the same size as X.
 'valid' - returns the portion of the convolution that is computed without the zero-padded edges.  In this situation, Z has 
size [xm-ym+1,xn-yn+1] when xm>=ym and xn>=yn.  Otherwise
conv2 returns an empty matrix.
 
 
If the full output is requested, then m ranges over 0 <= m < xm+ym-1
and n ranges over 0 <= n < xn+yn-1.  For the case where shape
is 'same', the output ranges over (ym-1)/2 <= m < xm + (ym-1)/2
and (yn-1)/2 <= n < xn + (yn-1)/2.