On 19 Dec 2004 03:04:15 -0800, "Rahul" <[EMAIL PROTECTED]> wrote:
>HI. >I want to compute dot product of two vectors stored as lists a and b.a >and b are of the same length. > >one simple way is >sum(a[i]*b[i] for i in range(len(a))) > >another simple way is >ans=0.0 >for i in range(len(a)): >ans=ans+a[i]*b[i] > >But is there any other way which is faster than any of the above. (By >the way profiling them i found that the second is faster by about 30%.) >rahul > Don't know about the timing, but another way: >>> import operator >>> a, b = range(5), range(5,10) >>> sum(map(operator.mul, a, b)) 80 Checking... >>> class OpShow(object): ... def __init__(self): self.tot = 0 ... def __call__(self, x, y): ... prod = x*y ... self.tot += prod ... print '%3s * %-3s => %s (tot %s)' %(x, y, prod, self.tot) ... return prod ... >>> sum(map(OpShow(), a, b)) 0 * 5 => 0 (tot 0) 1 * 6 => 6 (tot 6) 2 * 7 => 14 (tot 20) 3 * 8 => 24 (tot 44) 4 * 9 => 36 (tot 80) 80 Regards, Bengt Richter -- http://mail.python.org/mailman/listinfo/python-list
