Generate random numbers matrix - opencv

I want to know how can I generate a matrix of random numbers of any given size, for example say 2x4. Matrix should consists of signed whole number(range:-500 to +500). I have read the documentation of RNG, but I am not sure on how I should use this.

I referred too this question but this did not provide me the solution I am looking for.

I know this might be a silly question, but any help on it would be truly appreciated.

Thank you in advance.