This function is only used for documentation generation.
optimal_multiple_generic(rho, alpha, n2min, n2max, stepn2, fixed)
No return value
correlation between the two endpoints
one-sided significance level/family-wise error rate
minimal total sample size in phase II, must be divisible by 3
maximal total sample size in phase II, must be divisible by 3
stepsize for the optimization over n2, must be divisible by 3
assumed fixed treatment effect