srandbit.m

数字通信第四版原书的例程

function [sys, x0, str, ts] = srandbit(t, x, u, flag, n, prob, seed)
%SRANDDBIT outputs a zero vector with random bit ones.
%       This block outputs outputs a zero vector with ones in the vector.
%    	The probability of ones in the vector is controlled by the input
%	    vector prob.

%       Wes Wang
%       Copyright (c) 1995-96 by The MathWorks, Inc.

if flag == 3
    sys = zeros(1, n);
    len_prob = length(prob);
    dividing = prob(len_prob);
    if len_prob > 1
        for i = 1 : len_prob - 1
            dividing = [dividing(1) + prob(len_prob - i), dividing];
        end;
    end;        
    indx = find(dividing >= rand(1,1));
    if ~isempty(indx)
        for i = 1 : length(indx)
            ind_zeros = find(sys == 0);
            len_ind_zeros = length(ind_zeros);
            if len_ind_zeros > 1
                % assign zeros
                div_zeros = [0 : len_ind_zeros-1]/len_ind_zeros;
                ind_loc = find(div_zeros <= rand(1,1));
                sys(ind_zeros(length(ind_loc))) = 1;
            end;
        end;
    end;
elseif flag == 0
    rand('uniform');
    rand('seed',seed');
    sys(1) = 0;
    sys(2) = 0;
    sys(3) = n;
    sys(4) = 0;
    sys(5) = 0;
    sys(6) = 1;
    sys(7) = 1;
    x0 = [];
    ts = [-1. 0];
else
    sys = [];
end;