#include "pdefs.h"

/***************************************************/
/*	Calculate the cross sections for the given gas. */
/*	The values are at every eV starting at 0 eV.		*/

xsect()
{
	int i;
	
	/* elastic cross section */
   for (i=0; i<NEMAX; i++)
	{
		if (i <= elsengy0) 
			sels[i] = 0;
		else if (i > elsengy0 && i <= elsengy1)
			sels[i] = selsmax*(i - elsengy0)/(elsengy1 - elsengy0);
		else if (i > elsengy1 && i <= elsengy2)
			sels[i] = selsmax;
		else					
			sels[i] = selsmax*elsengy2/log(elsengy2)*log(i)/i;
   }

	/* excitation cross section */
   for (i=0; i<NEMAX; i++)
	{
		if (i <= extengy0) 
			sext[i] = 0;
		else if (i > extengy0 && i <= extengy1)
			sext[i] = sextmax*(i - extengy0)/(extengy1 - extengy0);
		else if (i > extengy1 && i <= extengy2)
			sext[i] = sextmax;
		else					
			sext[i] = sextmax*extengy2/log(extengy2)*log(i)/i;
   }

	/* ionization cross section */
	for (i=0; i<NEMAX; i++)
	{
		if (i <= ionengy0) 
			sion[i] = 0;
		else if (i > ionengy0 && i <= ionengy1)
			sion[i] = sionmax*(i - ionengy0)/(ionengy1 - ionengy0);
		else if (i > ionengy1 && i <= ionengy2)
			sion[i] = sionmax;
		else					
			sion[i] = sionmax*ionengy2/log(ionengy2)*log(i)/i;
	}
}