[SciPy-User] frequency components of a signal buried in a noisy time domain signal

Ivo Maljevic ivo.maljevic@gmail....
Sat Feb 27 13:03:07 CST 2010


Another suggestion, and this one also makes the parallel to Matlab. Make
sure it works for vectors:

>>> a=np.array([7,11,250])
>>> nextpow2(a)
array([ 3.,  4.,  8.])



On 27 February 2010 13:58, Ivo Maljevic <ivo.maljevic@gmail.com> wrote:

> I am sorry guys, but the solution I've proposed, and the one that was
> proposed by the scipy camp would cause confusion for those who switch from
> Matlab, and I just checked that.
> If you are going to use the same name as the Matlab one, than this function
> should return the m such that 2**m >= abs(n), and should not return 2^m.
>
> Whatever approach you guys want to use (and I believe that especially given
> what the function should return), do not return 2**m, but just m instead.
> For example:
>
> >>> def nextpow2(n):
> ...   return np.ceil(np.log2(n))
> ...
> >>> m=nextpow2(1000)
> >>> m
> 10.0
> >>> 2**m
> 1024.0
>
>
>
> On 27 February 2010 13:45, Robert Kern <robert.kern@gmail.com> wrote:
>
>> On Sat, Feb 27, 2010 at 12:41,  <josef.pktd@gmail.com> wrote:
>> > On Sat, Feb 27, 2010 at 1:31 PM, Charles R Harris
>> > <charlesr.harris@gmail.com> wrote:
>> >>
>> >> On Sat, Feb 27, 2010 at 11:02 AM, Robert Kern <robert.kern@gmail.com>
>> wrote:
>> >>>
>> >>> On Sat, Feb 27, 2010 at 04:02, Ivo Maljevic <ivo.maljevic@gmail.com>
>> >>> wrote:
>> >>> > David,
>> >>> > Nice way of avoiding log2, but how do you determine the length of
>> your
>> >>> > tab
>> >>> > array?
>> >>>
>> >>> The input arrays can only be so large. Even on 64-bit machines, the
>> >>> table need not have more than 64 entries.
>> >>>
>> >>>  tab = 2 ** np.arange(np.iinfo(np.intp).bits)
>> >>>
>> >>
>> >> Or
>> >>
>> >> tab = 1 << arange(iinfo(intp).bits - 1)
>> >
>> > I think I prefer a readable solution to this for calls that are not in
>> > an inner loop.
>> >
>> > scipy.signal.fftconvolve uses the same as Ivo's solution
>> >
>> > <<  means it's much larger than 1 ?
>>
>> It's a bitshift operator. Basically "x << y" means "x * (2 ** y)" for
>> integer arguments.
>>
>> --
>> 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
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>>
>
>
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