what is the use of seed.
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(1)
for k=1:3
rand('seed',k);
a=rand(1,5)
end
or (2)
for k=1:3
rand(k);
a=rand(1,5)
end
what is the difference between above two command.
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Answers (1)
Wayne King
on 27 Nov 2011
(1) is seeding the random number generator so that it produces a predictable sequence of "random" numbers.
For example, if you run the following loop again and again
for k = 1:3
rand('seed',k);
a = rand(5,1),
end
you will get the same 3 vectors for the variable, a.
In (2), rand(k) is producing a kxk matrix of uniform random numbers, then producing a 1x5 vector of uniform random numbers. So I'm not sure what the point of (2) is.
3 Comments
Walter Roberson
on 27 Nov 2011
Seeding in a loop is seldom desirable, and can often reduce randomness, and is not an acceptable mechanism for security. There have been successful attacks against systems that used seeding in a loop to try to implement security.
Seeding _before_ a loop can be useful.
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