ntaxa.py

import sys
import decimal
from math import factorial

usage = "\nUsage:   python ntaxa.py   {# of taxa}\n"

if __name__ == '__main__':
	ntaxa = 0
	if len(sys.argv) == 2:
		ntaxa = int( sys.argv[1] )
		if ntaxa < 2:
			print("%s" % usage)
			sys.exit(86)
	else:
		print("%s" % usage)
		sys.exit(86)

	d2 = decimal.Decimal( 2.0 )
	d3 = decimal.Decimal( 3.0 )
	d5 = decimal.Decimal( 5.0 )
	dn = decimal.Decimal( ntaxa )
	ctx = decimal.getcontext()
	ctx.prec = 8

	print("Parameters: ntaxa=%s" % (dn))
	A = factorial( ( d2 * dn ) - d3 )
	B = ctx.power( d2, ( dn - d2 ) )
	C = factorial( dn - d2 )
	result = A / ( B * C )
	print("# of rooted trees = %s" % result)
	A = factorial( ( d2 * dn ) - d5 )
	B = ctx.power( d2, ( dn - d3 ) )
	C = factorial( dn - d3 )
	result = A / ( B * C )
	print("# of unrooted trees = %s" % result)
	sys.exit(0)