functions in convol.i -

             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

             fft_good(n)  
 
     returns the smallest number of the form 2^x*3^y*5^z greater  
     than or equal to n.  An fft of this length will be much faster  
     than a number with larger prime factors; the speed difference  
     can be an order of magnitude or more.  
     For n>100, the worst cases result in a little over a 11% increase  
     in n; for n>1000, the worst are a bit over 6%; still larger n are  
     better yet.  The median increase for n<=10000 is about 1.5%.