帮忙解释下程序

骨头男

loop(p,I->p)
{
   p->flow_rate = 1.e-4;  
   P_DIAM(p) = 1.e-5 + fabs(cheap_gauss_random())*1.e-3;
   P_RHO(p) = 1.0;
   P_MASS(p) = P_RHO(p)*M_PI*pow(P_DIAM(p),3.0)/6.0;
}
}
哪位大哥帮忙解释下