Lab 11: Tuesday May 6, 2014

• Note that there are several example codes in the class repository that might be useful, e.g.

  • $UWHPSC/codes/openmp
  • $UWHPSC/codes/lapack/random
  • $UWHPSC/2013/homeworks
  • $UWHPSC/2013/solutions

• Discussion of random number generators. See UWHPSC/labs/lab11

• Questions about OpenMP?

Programming problem

Work on this in groups!

1. Write a Fortran program to do the following:

   • input seed and n from the command line
   • seed the random number generator using init_random_seed from the random_util.90 module,
   • generate an array x of n random numbers
   • compute the mean of these values: the sum of all elements of x divided by n. Do this with a do loop.

   Since random_number produces numbers that should be uniformly distributed between 0 and 1, the mean should be approximately 0.5 for large n. It can also be shown that for a uniform distribution, the difference between the mean of a sample of n numbers and the true mean of the distribution should decay to zero like \(1/\sqrt{n}\) as \(n\longrightarrow\infty\). Do you observe this?

2. Modify your code to use OpenMP by using an omp parallel do loop with a suitable reduction to compute the mean.

3. There is a quiz for this lab.