COSMO_PARAM

     Derive full set of cosmological density parameters from a partial set

     This procedure is called by LUMDIST and GALAGE to allow the user a choice
     in defining any two of four cosmological density parameters.
     Given any two of the four input parameters -- (1) the normalized matter
     density Omega_m (2) the normalized cosmolgical constant, Omega_lambda (2) the normalized
     curvature term, Omega_k and (4) the deceleration parameter q0 --  this
     program will derive the remaining two.     Here "normalized" means divided by the closure
     density so that Omega_m + Omega_lambda + Omega_k = 1.    For a more
     precise definition see Caroll, Press, & Turner (1992, ArAA, 30, 499).
     If less than two parameters are defined, this procedure sets default
     values of Omega_k=0 (flat space), Omega_lambda = 0.7, Omega_m = 0.3
     and q0 = -0.5

       COSMO_PARAM, Omega_m, Omega_lambda, Omega_k, q0
 INPUT-OUTPUTS:
     Omega_M - normalized matter energy density, non-negative numeric scalar
     Omega_Lambda - Normalized cosmological constant, numeric scalar
     Omega_k - normalized curvature parmeter, numeric scalar.   This is zero
               for a flat universe
     q0 - Deceleration parameter, numeric scalar = -R*(R'')/(R')^2
          = 0.5*Omega_m - Omega_lambda

     If more than two parameters are defined upon input (overspecification),
     then the first two defined parameters in the ordered list Omega_m,
     Omega_lambda, Omega_k, q0 are used to define the cosmology.

     Suppose one has Omega_m = 0.3, and Omega_k = 0.5 then to determine
     Omega_lambda and q0
       IDL> cosmo_param, 0.3, omega_lambda, 0.5, q0
       which will return omega_lambda = 0.2 and q0 = -2.45

       W. Landsman         Raytheon ITSS         April 2000

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