randbit.m

数字通信第四版原书的例程

function out = randbit(n, m, prob, seed);
%RNADBIT Binary noise generator.
%       OUT = RANDBIT(N, M) generates an N-by-M zero matrix with an single 
%       "1" randomly placed in any bit of each row. 
%
%       OUT = RANDBIT(N, M, PROB) generates an N-by-M zeros matrix with "1"s
%       uniformly distributed in any bit of each row. The probability of "1"
%       appearance is specified in variable PROB. The first element of PROB
%       is the probability of single "1" in each row. The second element of
%       PROB is the probability of double "1" in each row and so on. The size
%       of vector prob is the maximum "1" bit in each row. The sum of the 
%       PROB cannot be larger than one. 
%
%       OUT = RANDBIT(N, M, PROB, SEED) specify the seed.
%
%       This function is initially designed to test error-control coding.
%
%       See also: RANDINT.

%       Wes Wang 8/8/94, 10/11/95.
%       Copyright (c) 1995-96 by The MathWorks, Inc.
%       $Revision: 1.1 $  $Date: 1996/04/01 18:02:02 $

if nargin < 2
    error('Not enough input variable for RANDINT')
elseif nargin < 3
    prob = 1;
end;

if nargin < 4
    % assign a seed if the user has not assigned one.
    seed = floor(sum([n, m, prob(:)'*100]) * 123);
end;

rand('uniform');
rand('seed',seed');
out = zeros(n, m);

len_prob = length(prob);
if len_prob > m
    len_prob = m;
end;

dividing = prob(len_prob);
if len_prob > 1
    for i = 1 : len_prob-1
        dividing = [dividing(1)+prob(len_prob-i), dividing];
    end;
end;

if dividing(len_prob) > 1
    error('The sum of the probability cannot be larger than one')
end;

x1 = rand(n, 1);
for i = 1 : n
    % iterative for each row
    indx = find(dividing >= x1(i));
    if ~isempty(indx)
        for j = 1 : length(indx)
            ind_zeros = find(out(i, :) == 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));
                out(i, ind_zeros(length(ind_loc))) = 1;
            end;
        end;
    end;
end;

% -- end of randbit --