PythonQ 240-8XX Instrukcja Użytkownika Pobierz pdf (Strona 20)

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Array computat ion s

Arithmetic operations can be used with arrays:

b=3

a-1 #aisarray,bbecomesarray

1) compute t1 = 3

a,2)computet2= t1 - 1,3)setb=t2

Array operations are much faster than element-wise operations:

>>> import time # module for measuring CPU time

>>> a = linspace(0, 1, 1E+07) # create some array

>>> t0 = time.clock()

>>> b = 3

a-1

>>> t1 = time.clock() # t1-t0 is the CPU time of 3

a-1

>>> for i in xrange(a.size): b[i] = 3

a[i] - 1

>>> t2 = time.clock()

>>> print ’3

a-1: %g sec, loop: %g sec’ % (t1-t0, t2-t1)

a-1: 2.09 sec, loop: 31.27 sec

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PythonQ 240-8XX Instrukcja Użytkownika Strona 20