what is the use of seed.

(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.

Answer 1

[Wayne King]

(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.

[SANJEEV KUMAR]

thanks.......

[Walter Roberson]

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.

[Daniel Shub]

The 'seed' method is pretty dated at this point.