sage-support is one of the best list. English is not my mother language and 
sometimes I don't explain myself well but always people here are very kind 
and trying to help... It's very important this can long !

Le vendredi 14 septembre 2018 18:00:55 UTC+2, Peter Luschny a écrit :
>
> How can I speed up this computation?
>
>     H.<i,j,k> = QuaternionAlgebra(SR, -1, -1)
>     def Q(a, b, c, d): return H(a + b*i + c*j + d*k)
>     def P(n): return Q(x+1,1,1,1)*P(n-1) if n > 0 else Q(1,0,0,0)
>     def p(n): return P(n)[0].list()
>     for n in (0..20): print [n], p(n)
>
>     [0] [1]
>     [1] [1, 1]
>     [2] [-2, 2, 1]
>     [3] [-8, -6, 3, 1]
>     [4] [-8, -32, -12, 4, 1]
>     [5] [16, -40, -80, -20, 5, 1]
>     [6] [64, 96, -120, -160, -30, 6, 1]
>     ...
>
> With Mathematica this takes 6 sec, with Sage it takes 
> hours, (in fact I interrupted after n=15). 
>
> Thanks, Peter
>
>
>

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