[SciPy-Dev] Maximum length sequence

[Neal Becker]

Robert Kern wrote:

> On Wed, Feb 19, 2014 at 1:37 PM, Neal Becker <ndbecker2 at gmail.com> wrote:
>> Eric Larson wrote:
>>
>>> Maximum length sequences (MLS) are useful in signal processing for finding
>>> impulse responses. I can't find a great implementation of MLS in Python,
>>> but maybe I've missed one somewhere. Would this be something good to put in
>>> scipy.signal, perhaps as scipy.signal.mls?
>>>
>>> Cheers,
>>> Eric
>>
>> If you want a sequence of gaussian rv, just use numpy.random.
> 
> That does not appear to be what he wants:
> 
> http://en.wikipedia.org/wiki/Maximum_length_sequence
> 

I'm assuming what's wanted here is white noise.

To generate random bits of some specified bit width, I use the underlying
mersenne twister to generate uniform integer r.v., then cache the bits (32 at a 
time) and output them with the desired width.

Of course this is not identical to what the OP asked, but serves the same 
purpose.

A snippet of the C++ code used for this looks like:

    template<class Engine>
    result_type operator() (Engine& eng) {


      if (count <= width-1) {
	cache = eng();
	count = std::min (std::numeric_limits<typename 
Engine::result_type>::digits, std::numeric_limits<result_type>::digits);
      }
      result_type bits = cache & mask;
      cache >>= width;
      count -= width;
      return bits;
    }