There's the same precondition in IBM XL C/C++ V9.0 for AIX too: [quote from docs at http://tinyurl.com/6xpdtt ] mersenne_twister::seed template<class Gen> void seed(Gen& gen); void seed() {seed(5489); } void seed(unsigned long x0); Precondition: 0 < x0 The first seed function generates N values from the values of type unsigned long returned by successive invocations of gen and then twists the resulting large integer value. Each value is gen() % 2W. The second seed function calls seed(4357). The third seed function sets the oldest historical value h[0] to x0 mod 2W, then iteratively sets each successive historical value h[i] to (i + 1812433253 * (h[i - 1] >> (W - 2))) mod 2W, for i ranging from 1 to N - 1. [/quote] regards Gunther