function P = pressure(h)

%	This is the pressure calculator as a function of height.  It is based on the US 
%	Standard Atmosphere of 1976.
%	Source: http://scipp.ucsc.edu/outreach/BALLOON/Atmosphere/1976%20Standard%20Atmosphere.htm
%
%  This function is at least in the SECOND ORDER phase of development.

%	VARIABLES and UNITS
%
%	conventions:	Large arrays are in all caps
%						Vectors and other variables are in mixed case, as appropriate
%
%	h					:The height above sea level, in m.
%  P					:Pressure of the atmosphere at height h, in N/m2.
%	P_o				:Pressure of the atmosphere at sea level, in N/m2.



global data;
global index;


%	CONSTANTS
P_o = data(1,91);		% N/m2 



% MAIN PROGRAM
   
if (h <= 11000)
   P = P_o * (1 - h / 44329)^5.255876;
   
elseif (h <= 20000)
   P = P_o * (0.223361)*exp((10999-h)/6341.4);
   
elseif h <= 32000
   P = P_o * (0.988626 + h/198903)^(-34.16319);
   
elseif h <= 47000
   P = P_o * (0.898309 + h/55280)^(-12.20114);
   
elseif h <= 51000
   P = P_o *  (0.00109456)*exp((46998-h)/7922);
   
elseif h <= 71000
   P = P_o * (0.838263 - h/176142)^12.20114;
   
else 
   P = P_o * (0.838263 - h/176142)^12.20114;			% same as <=71000
   
end


data(index,91) = P;