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function [seed,whichGen] = ClockRandSeed(seed,whichGen)
% [seed,whichGen] = ClockRandSeed([seed],[whichGen])
%
% ClockRandSeed seeds the random number from the time-of-day clock. If seed
% is passed this is used instead.
%
% The multiplier 1e6 in fix(1e6*sum(clock)) is bigger than the 100
% suggested by Mathworks (see help RAND). They suggest 100*sum(clock), but
% this would only change the seed once every 1/100 sec, which might
% correspond to many iterations of a loop. With the bigger multiplier it's
% pretty sure (depending only on clock grain) that two successive calls
% will generate different seeds.
%
% Also unlike the Mathworks suggestion (see help RAND), we call FIX. This
% has no effect on RAND and RANDN, but makes it easier to correctly print
% the seed to a file. When a random seed generates an interesting result
% one would like to be able to recreate the conditions that generated the
% run. If the seed 1e6*sum(clock) is printed to a file, '%.0f' will often
% round it differently than RAND would.
%
% Note in that in Matlab 5 there are two random number generators, the
% Matlab 5 generator and the Matlab 4 generator. (Matlab 4
% has only the version 4 generator.) ClockRandSeed checks what version of
% Matlab you're running and uses the version 5 generator if it can. The
% string whichGen contains 'seed' for the version 4 generator and 'state'
% for the version 5 generator.
%
% See also: rand, randn.
% 10/15/93 dhb Made this a function.
% 4/11/94 dhb Added randn seeding.
% 8/9/97 dgp Update for more reliable seed.
% dgp Gutted it to make version-dependence explicit.
% 8/9/97 dhb Ungutted it to hide version-dependence.
% 8/13/97 dhb Optional return of which generator used and passing of seed/generator.
% 7/24/04 awi Cosmetic.
% 1/29/05 dgp Cosmetic.
if (nargin == 0)
seed = fix(1e6*sum(clock));
if sscanf(version,'%f',1)<5
whichGen = 'seed';
else
whichGen = 'state';
end
elseif (nargin == 1)
if (isempty(seed))
seed = fix(1e6*sum(clock));
end
if sscanf(version,'%f',1)<5
whichGen = 'seed';
else
whichGen = 'state';
end
else
if (isempty(seed))
seed = fix(1e6*sum(clock));
end
if (isempty(whichGen))
if sscanf(version,'%f',1)<5
whichGen = 'seed';
else
whichGen = 'state';
end
end
end
rand(whichGen,seed);randn(whichGen,seed);
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