So, I have a pretty simple code but I need to keep one variable (xg_z) from ever being below zero (the math will allow that to happen but physical reality will not). I thought I just needed an if-then (see in code; last 4 lines), but when I check it, it still lets the variable go below zero … which screws up all the other calculations I need to make based on the value.
Any idea what I'm doing wrong?
if true % code
% Constants:
density_1 = 2830; zStart = 6000; % depth in crust (m)
zEnd = 0; % depth in crust (m) rhoc = 2650; % density of the crust (kg m^-3)
xo = 0.045; % initial quantity of dissolved gas
rhom0 = density_1; % Initial density of the magma (or saturated density)
Q_in = 2.3; % Volume flux of magma into the system [m^3s^-1]
t_flux = 35.*24.*60.*60; % Days of magma flux into the system (35) [s]
mass_initial = density_1./(Q_in.*t_flux); % density / volume to get initial mass of magma
volume_final = (Q_in.*t_flux); % Volume actually cancels and is unecessary
% Depth range
z = zEnd:10:zStart; % Total range from chamber top to surface
z2 = 1200:10:6000; % Range from chamber to conduit
z3 = 0:10:1200; % Range from conduit to surface
% Constants: rhog = 0.804; % density of gas [kg m^-3]
s = 4.11.*(10.^-6); % empirical coefficient depending on gas compositions of gas & melt
n = 0.5; % empirical coefficient depending on gas compositions of gas & melt Psurface = 101325; % pressure at Earth's surface [Pa]
g = 9.8; % acceleration due to gravity [m s^-2]
rhow = 1000; % density of water [kg m^-3]
% Variables:
P_z = Psurface + (rhoc.*z.*g); % Pressure as a function of depth [Pa]
xg_z = xo - (s.*P_z.^n); % gas in vapor form as a function of z
if(xg_z<0) xg_z=0;end
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