int freesteam_region_pu(double p, double u){
double p13 = freesteam_region4_psat_T(REGION1_TMAX);
if(p < p13){
double Tsat = freesteam_region4_Tsat_p(p);
double uf = freesteam_region1_u_pT(p,Tsat);
if(u < uf)return 1;
double ug = freesteam_region2_u_pT(p,Tsat);
if(u > ug)return 2;
return 4;
}
double u13 = freesteam_region1_u_pT(p,REGION1_TMAX);
if(u < u13){
return 1;
}
double T23 = freesteam_b23_T_p(p);
double u23 = freesteam_region2_u_pT(p,T23);
if(u > u23){
return 2;
}
if(p > IAPWS97_PCRIT)return 3;
/* FIXME what we really need here is a psat(u) function! The current method
is singular. */
double Tsat = freesteam_region4_Tsat_p(p);
double rhof = freesteam_region4_rhof_T(Tsat);
double uf = freesteam_region3_u_rhoT(rhof,Tsat);
if(u<uf) return 3;
double rhog = freesteam_region4_rhog_T(Tsat);
double ug = freesteam_region3_u_rhoT(rhog,Tsat);
if(u>ug)return 3;
return 4;
}
double freesteam_region4_u_Tx(double T, double x){
double uf, ug;
if(T < REGION1_TMAX){
double psat = freesteam_region4_psat_T(T);
uf = freesteam_region1_u_pT(psat,T);
ug = freesteam_region2_u_pT(psat,T);
}else{
double rhof, rhog;
rhof = freesteam_region4_rhof_T(T);
rhog = freesteam_region4_rhog_T(T);
uf = freesteam_region3_u_rhoT(rhof,T);
ug = freesteam_region3_u_rhoT(rhog,T);
}
return uf + x*(ug - uf);
}