[SciPy-user] [newb] how to create arrays

Robert Kern robert.kern@gmail....
Thu Jan 3 06:08:19 CST 2008


Neal Becker wrote:
> Robert Kern wrote:
> 
>> Anne Archibald wrote:
>>> On 02/01/2008, Neal Becker <ndbecker2@gmail.com> wrote:
>>>> How would I create a vector of complex random variables?
>>>>
>>>> I'm thinking the best way is to create a complex vector, then
>>>> assign to the real and imag parts (using e.g., random.standard_normal).
>>>>
>>>> I don't see any way to create an uninitialized array.  I guess I'd have
>>>> to
>>>> use zeros?  Is there any way to avoid the wasted time of initializing
>>>> just to write over it?
>>> You can create an uninitialized array if you want to. But, from your
>>> question, you may well be thinking about your problem in the wrong
>>> way. If all you want to do is store a whole bunch of values you
>>> compute in a loop, use a python list.
>> In this case, he wouldn't be using a loop.
>>
>>   from numpy import *
>>
>>   z = empty([10], dtype=complex)
>>   z.real[:] = random.standard_normal(10)
>>   z.imag[:] = random.standard_normal(10)
>>
> 
> This is what I had in mind.
> 
> I guess there isn't something that could do this in a single step, something
> like:
> 
> z = random.standard_normal(10) + i * random.standard_normal(10)

Sure:

  z = random.standard_normal(10) + 1j * random.standard_normal(10)

There's a minor tradeoff wrt the temporary; if your arrays are large enough for
you to be concerned about the overhead of zeros() over empty(), you might be
concerned about it as well.

-- 
Robert Kern

"I have come to believe that the whole world is an enigma, a harmless enigma
 that is made terrible by our own mad attempt to interpret it as though it had
 an underlying truth."
  -- Umberto Eco


More information about the SciPy-user mailing list