| convol 
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             convol(a,b)  
 
     returns convolution of vector a with vector b, a vector  
     of length na+nb-1 where na=numberof(a), nb=numberof(b).  
     In detail, for i=[1 to na+nb-1]  
       result(i) = sum j=[max(1,1+i-nb) to min(na,i)] (a(j)*b(1+i-j))  
     The n0= and n1= keywords can be used to control the section of  
     the full array that is actually returned, 1<=n0 line 6  
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