/*e2 second exponential integral */
#include "cddefines.h"
#include "e2.h"

double e2(double t, 
	  double tln)
{
	double e2_v, 
	  remain;

#	ifdef DEBUG_FUN
	fputs( "<+>e2()\n", debug_fp );
#	endif

	/* fit of second exponential integral;
	 * T is optical depth, and TLN is EXP(-t)
	 * */
	if( t < 0.3 )
	{
		remain = (1.998069357 + t*(66.4037741 + t*107.2041376))/(1. + 
		  t*(37.4009646 + t*105.0388805));

	}
	else if( t < 20. )
	{
		remain = (1.823707708 + t*2.395042899)/(1. + t*(2.488885899 - 
		  t*0.00430538));

	}
	else
	{
		remain = 1.;
	}

	e2_v = remain*tln/(2. + t);


#	ifdef DEBUG_FUN
	fputs( " <->e2()\n", debug_fp );
#	endif
	return( e2_v );
}