list comprehension question

[88888 Dihedral]

Dave Angel於 2012年10月17日星期三UTC+8下午10時37分01秒寫道：
> On 10/17/2012 10:06 AM, rusi wrote:
> 
> > On Oct 17, 5:33 pm, Dave Angel <d... at davea.name> wrote:
> 
> >> On 10/17/2012 12:43 AM, Kevin Anthony wrote:> Is it not true that list comprehension is much faster the the for loops?
> 
> >>
> 
> >>> If it is not the correct way of doing this, i appoligize.
> 
> >>> Like i said, I'm learing list comprehension.
> 
> >> list comprehensions CAN be much faster, but not necessarily.  The most
> 
> >> complex a loop, the less likely it'll help much.
> 
> > One-lining the comprehension seems to make a difference of about 10%
> 
> > out here. Maybe Ive missed something? Seems too large�
> 
> >
> 
> > # My original suggestion
> 
> > def dot(p,q): return sum (x*y for x,y in zip(p,q))
> 
> > def transpose(m): return zip(*m)
> 
> > def mm(a,b): return mmt(a, transpose(b))
> 
> > def mmt(a,b): return [[dot(ra, rb) for rb in b] for ra in a]
> 
> >
> 
> > # One-liner (Thanks Hans for reminding me of sum)
> 
> >
> 
> > def mm1(a,b): return [[sum([x*y for x,y in zip(ra,rb)]) for rb in
> 
> > zip(*b)] for ra in a]
> 
> >
> 
> >>>> t1=Timer("res=mm1(m,m)", setup="from __main__ import mm1, m")
> 
> >>>> t1.timeit(1000)
> 
> > 12.276363849639893
> 
> >>>> t0=Timer("res=mm(m,m)", setup="from __main__ import mm, m")
> 
> >>>> t0.timeit(1000)
> 
> > 13.453603029251099
> 
> 
> 
> And I'd wager all the improvement is in the inner loop, the dot() function.
> 
> 
> 
> 
> 
> -- 
> 
> 
> 
> DaveA

Thanks for the tips of matrix operations over some fields or rings 
other than the real field and the complex field.