Generating arrays of random numbers without loop in MATLAB

Question

I have a loop which generates random samples from the chi-square distribution with different degrees of freedom (df1, df2, df3, df4) and saves it to a cell array:

for k=1:N
x{k} = chi2rnd([df1 df2 df3 df4]);
end

Is there any way to do this without any iterations? I tried to use cellfun, but it didn't work.

Answer 1

Here is a vectorized way (method 1):

x = num2cell(chi2rnd(repmat([df1 df2 df3 df4], N, 1), N, 4), 2);

You may also try this method (method 2):

df = [df1 df2 df3 df4];
y = zeros(N,numel(df));
for k = 1:numel(df)
  y(:,k) = chi2rnd(df(k),N,1);
end
x = num2cell (y,2);

Result of timing for N = 10000 in Octave. However you need to measure the time in MATLAB:

Original solution :              3.91095 seconds
Vectorized solution (method 1):  0.0691321 seconds
Loop solution (method 2) :       0.0124869 seconds