tau.py

'''
Functions for calculating tau parameters from coordination angles
The functions can be used directly for calculations or the combined 'tau' function can be used
Christopher Varjas (November 2017)
'''
import math

theta = math.degrees(math.acos(-1 / 3))
# theta = 109.5


def tau5(b, a):
	return (b - a) / 60


def tau4(b, a):
	return (360 - (a + b)) / (360 - (2 * theta))


def tau4prime(b, a):
	return ((b - a) / (360 - theta)) + ((180 - b) / (180 - theta))


def tau(angles, ligands=None):
	'''
	Angles expects a list
	If all angles are defined, the correct tau 4 or 5 function will be selected
	Or the number of ligands can be defined with the second parameter as an integer with only a few angles included in the list
	'''
	# Sort angles that were input
	angles.sort(reverse=True)
	# If ligands is defined, use the appropriate function
	if ligands == 5:
		return tau5(angles[0], angles[1])
	elif ligands == 4:
		return tau4prime(angles[0], angles[1])

	# If ligand count was not defined, try to determine if all angles are defined
	if len(angles) == 10:
		return tau5(angles[0], angles[1])
	elif len(angles) == 6:
		return tau4prime(angles[0], angles[1])
	else:
		print('Need to define all complex angles, or set the calculation type to 4 or 5')
		return False