/*fhummr evaluate Hummer's betaF(beta) function */
#include "cddefines.h"
#include "fhummr.h"

double fhummr(double beta) /* beta is ratio of continuum to mean line opacity,
									 * returns dest prob = beta F(beta) */
{
	double fhummr_v, 
	  x;

#	ifdef DEBUG_FUN
	fputs( "<+>fhummr()\n", debug_fp );
#	endif

	/* evaluates Hummer's F(beta) function for case where damping
	 * constant is zero, are returns beta*F(beta)
	 * fit to Table 1, page 80, of Hummer MNRAS 138, 73-108.
	 * beta is ratio of continuum to line opacity; FUMMER is
	 * product of his F() times beta; the total destruction prob
	 * this beta is Hummer's normalization of the Voigt function */

	assert( beta >= 0.) ;/* non-positive is unphysical */
	if( beta <= 0. )
	{
		fhummr_v = 0.;
	}
	else
	{
		x = log10(beta);
		if( x < -5.5 )
		{
			fhummr_v = 3.8363 - 0.56329*x;
		}
		else if( x < -3.5 )
		{
			fhummr_v = 2.79153 - 0.75325*x;
		}
		else if( x < -2. )
		{
			fhummr_v = 1.8446 - 1.0238*x;
		}
		else
		{
			fhummr_v = 0.72500 - 1.5836*x;
		}
		fhummr_v *= beta;
	}


#	ifdef DEBUG_FUN
	fputs( " <->fhummr()\n", debug_fp );
#	endif
	return( fhummr_v );
}