# Description:
#   Removes all nodal points not appearing in the element array.
#
# Arguments:
#   p		Nodal points (matrix of size (Npts x 4)).
#	tri		Element array (matrix of size (Nel x 3) or (Nel x 5)).
#	edge	Boundary elements (matrix of size (Nel x 2) or (Nel x 4)).
#
# Returns:
#   p		The stripped down nodal array (smaller size).
#   tri		Updates nodal indexes of the element array (updated values).
#   edge	Updates nodal indexes of the boundary elements (updated values).
#
#   Author: Kjetil A. Johannessen, Abdullah Abdulhaque
#   Last edit: 07-10-2019


import numpy as np


def RemoveUnused_2D(p,tri,edge):
	tmp = tri[:,0:3]
	N = np.shape(p)[0]
	used = np.zeros(N)
	used[tmp.T.flatten()] = 1
	uu = []
	k = -1
	for i in range(0,N):
		k += 1
		if used[k] == 1:
			uu += [k]
	uu = np.sort(np.array(uu))

	Offset = np.zeros(N,dtype=np.int)
	TotOffset = 0
	k = 1
	for i in range(1,N+1):
		if (k <= len(uu)) and (uu[k-1] != i-1):
			TotOffset += 1
		else:
			k += 1
		Offset[i-1] = np.int(TotOffset)

	p = p[uu,:]
	Nel = np.shape(tri)[0]
	for i in range(0,Nel):
		tri[i,0:3] -= Offset[tri[i,0:3]]
	Nel = np.shape(edge)[0]
	for i in range(0,Nel):
		edge[i,0:2] -= Offset[edge[i,0:2]-1]

	return p,tri,edge