function a = setState_SP(a,sp)
% SETSTATE_SP    Set the specific entropy [J/kg/K] and pressure [Pa].
%
%    setState_SP(a, sp) sets the specific entropy and pressure
%    of object a, holding its composition fixed. Argument 'sp' must
%    be a vector of length 2 containing the desired values for the specific
%    entropy (J/kg/K) and pressure (Pa).
%
if sp(1) <= 0.0
    error('the specific entropy must be positive');
end
if sp(2) <= 0.0
    error('the pressure must be positive');
end
thermo_set(a.tp_id,23,sp);