Convolution and Cross Correlation Blackbox
Method#1: Feed input arguments that are asymmetrical:
&gt;&gt; conv(1:3,1:3)

ans =
     1     4    10    12     9   
&gt;&gt; xcorr(1:3,1:3)

ans =    
    3.0000    8.0000   14.0000    8.0000    3.0000

Method#2: Swap inputs and see if the output changes
&gt;&gt; xcorr(1:3,[1 1 1])
ans =
    1.0000    3.0000    6.0000    5.0000    3.0000
&gt;&gt; xcorr([1 1 1], 1:3)
ans =
    3.0000    5.0000    6.0000    3.0000    1.0000