On Sun, Dec 19, 2004 at 03:04:15AM -0800, Rahul 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
some numbers to confirm my previous reply:
1
zip: 0.00115 (1.00)
range: 0.00108 (0.94)
array: 0.00075 (0.65)
10
zip: 0.00306 (1.00)
range: 0.00288 (0.94)
array: 0.00074 (0.24)
100
zip: 0.02195 (1.00)
range: 0.02035 (0.93)
array: 0.00079 (0.04)
1000
zip: 0.21016 (1.00)
range: 0.19930 (0.95)
array: 0.00130 (0.01)
10000
zip: 4.98902 (1.00)
range: 2.70843 (0.54)
array: 0.01405 (0.00)
(the integers are the number of elements in a random array of floats;
'zip' refers to
sum([x*y for (x,y) in zip(a,b)])
'range', to
sum([a[i]*b[i] for i in range(len(a))])
and 'array' makes a and b Numeric's 'array' objects, with atlas
installed (and hence dotblas loading and assembler version of dot
tuned for the system's processor (in this case a pentium3)). The code
in this case is simply
Numeric.dot(a, b)
The advantage of atlas on systems with sse2 should be even greater.
--
John Lenton ([EMAIL PROTECTED]) -- Random fortune:
El deseo nos fuerza a amar lo que nos hará sufrir.
-- Marcel Proust. (1871-1922) Escritor francés.
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