Editing User:Markuman

* Owner of http://mxeoctave.osuv.de
* markuman@gmail.com (Mail, Gtalk)
* markuman@jabber.ccc.de (XMPP)
* markuman on irc.freenode.net 
* https://keybase.io/notagain
* https://github.com/markuman/

=== random ===

how to get equal matlab random numbers in octave - using twister(!) algorithm?

* terminology: https://en.wikipedia.org/wiki/Mersenne_twister#Pseudocode
* nice2know: http://stackoverflow.com/questions/13735096/python-vs-octave-random-generator

==== initial situation ====

* ruby and python using twister algo as default
* force twister algo in matlab and octave

====== octave ======

    octave:1> rand('twister',0)
    octave:2> rand
    ans =    0.844421851525048

====== python ======

    >>> import random
    >>> random.seed(0)
    >>> random.random()
    0.8444218515250481

====== numpy ======

    >>> import numpy
    >>> numpy.random.seed(0)
    >>> numpy.random.random()
    0.5488135039273248

====== ruby ======

    irb(main):001:0> prng = Random.new(0)
    => #<Random:0x00000001d469e8>
    irb(main):002:0> prng.rand()
    => 0.5488135039273248

====== matlab ======

    >> rand('twister',0)
    >> rand
     
    ans =
         
        0.548813503927325


==== how to get the right seed states in octave? ====

    rand('twister',0)
    states=rand('state'); 

seems to be the wrong ones. but they fit to them in python! ;)


    function ret = twister_seed(SEED=0)
    
        ret = uint32(zeros(625,1));
        ret(1) = SEED;
        for N = 1:623
            ## initialize_generator
            # bit-xor (right shift by 30 bits)
            uint64(1812433253)*uint64(bitxor(ret(N),bitshift(ret(N),-30)))+N; # has to be uint64, otherwise in 4th iteration hit maximum of uint32!
            ret(N+1) = uint32(bitand(ans,uint64(intmax('uint32')))); # untempered numbers
        endfor
        ret(end) = 1;   
     
    endfunction


    octave:1> rand('twister',twister_seed) # notice: default seed is 0 in the function
    octave:2> rand
    ans =    0.548813503927325
    octave:3> rand
    ans =    0.715189366372419
    octave:4> rand
    ans =    0.602763376071644

compare to matlab...

    >> rand('twister',0)
    >> rand
    
    ans =
    
       0.548813503927325
    
    >> rand
    
    ans =
    
       0.715189366372419
    
    >> rand
    
    ans =
    
       0.602763376071644



==== TODO ====

* Find the `seed` stuff in octave source