prbs_a
======

pseudo random binary sequences generation



Calling Sequence
~~~~~~~~~~~~~~~~


::

    [u]=prbs_a(n,nc,[ids])




Description
~~~~~~~~~~~

generation of pseudo random binary sequences `u=[u0,u1,...,u_(n-1)]` u
takes values in {-1,1} and changes at most nc times its sign. ids can
be used to fix the date at which u must change its sign ids is then an
integer vector with values in `[1:n]`.



Examples
~~~~~~~~


::

    u=prbs_a(50,10);
    `plot2d2`_("onn",(1:50)',u',1,"151",' ',[0,-1.5,50,1.5]);