create_pop: Creates a population with a specified correlation.
Description
The correlation will be exactly the one specified. The used method is
described here:
https://stats.stackexchange.com/questions/15011/generate-a-random-variable-with-a-defined-correlation-to-an-existing-variables/15040#15040
Usage
create_pop(rho, size)
Value
Two-dimensional population matrix with a specific correlation.