function g = gravity(z)


%	This function determines gravity as a funtion of height from sea level.
%	It is in the SECOND ORDER stage of development.

%	VARIABLES and UNITS
%	
%	conventions:	Large arrays are in all caps
%						Vectors and other variables are in mixed case, as appropriate
%
%	r_earth			:radius of the Earth constant, in m.
%	G					:Earth's gravitational constant, in Nm2/kg2.
%	M					:Mass of the Earth, in kg.
%	GM					:G*M to ease the calc load of the computer, in Nm2/kg.



global data;
global index;


%	CONSTANTS

r_earth = 6378140;			% m
G = 6.672E-11;					% Nm2/kg2
M = 5976E24;					% kg
GM = 3.9871872E14;			% Nm2/kg



%	MAIN PROGRAM

g = -1 * GM / (r_earth + z)^2;		% z down is negative in this coord system


data(index,96) = g;