# $Id$
##
##  This file is part of pyFormex 0.8.9  (Fri Nov  9 10:49:51 CET 2012)
##  pyFormex is a tool for generating, manipulating and transforming 3D
##  geometrical models by sequences of mathematical operations.
##  Home page: http://pyformex.org
##  Project page:  http://savannah.nongnu.org/projects/pyformex/
##  Copyright 2004-2012 (C) Benedict Verhegghe (benedict.verhegghe@ugent.be) 
##  Distributed under the GNU General Public License version 3 or later.
##
##
##  This program is free software: you can redistribute it and/or modify
##  it under the terms of the GNU General Public License as published by
##  the Free Software Foundation, either version 3 of the License, or
##  (at your option) any later version.
##
##  This program is distributed in the hope that it will be useful,
##  but WITHOUT ANY WARRANTY; without even the implied warranty of
##  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
##  GNU General Public License for more details.
##
##  You should have received a copy of the GNU General Public License
##  along with this program.  If not, see http://www.gnu.org/licenses/.
##
"""inertia.py

Compute inertia related quantities of a Formex.
This comprises: center of gravity, inertia tensor, principal axes

Currently, these functions work on arrays of nodes, not on Formices!
Use func(F,f) to operate on a Formex F.
"""
from __future__ import print_function

from numpy import *
from arraytools import normalize

def centroids(X):
    """Compute the centroids of the points of a set of elements.

    X (nelems,nplex,3)
    """
    return X.sum(axis=1) / X.shape[1]


def center(X,mass=None):
    """Compute the center of gravity of an array of points.

    mass is an optional array of masses to be atributed to the
    points. The default is to attribute a mass=1 to all points.

    If you also need the inertia tensor, it is more efficient to
    use the inertia() function. 
    """
    X = X.reshape((-1,X.shape[-1]))
    if mass is not None:
        mass = array(mass)
        ctr = (X*mass).sum(axis=0) / mass.sum()
    else:
        ctr = X.mean(axis=0)
    return ctr


def inertia(X,mass=None):
    """Compute the inertia tensor of an array of points.

    mass is an optional array of masses to be atributed to the
    points. The default is to attribute a mass=1 to all points.

    The result is a tuple of two float arrays:

      - the center of gravity: shape (3,)
      - the inertia tensor: shape (6,) with the following values (in order):
        Ixx, Iyy, Izz, Ixy, Ixz, Iyz 
    """
    X = X.reshape((-1,X.shape[-1]))
    if mass is not None:
        mass = array(mass)
        ctr = (X*mass).sum(axis=0) / mass.sum()
    else:
        ctr = X.mean(axis=0)
    Xc = X - ctr
    x,y,z = Xc[:,0],Xc[:,1],Xc[:,2]
    xx,yy,zz,yz,zx,xy = x*x, y*y, z*z, y*z, z*x, x*y
    I = column_stack([ yy+zz, zz+xx, xx+yy, -yz, -zx, -xy ])
    if mass is not None:
        I *= mass
    return ctr,I.sum(axis=0)


def principal(inertia,sort=False,right_handed=False):
    """Returns the principal values and axes of the inertia tensor.
    
    If sort is True, they are sorted (maximum comes first).
    If right_handed is True, the axes define a right-handed coordinate system.
    """
    Ixx,Iyy,Izz,Iyz,Izx,Ixy = inertia
    Itensor = array([ [Ixx,Ixy,Izx], [Ixy,Iyy,Iyz], [Izx,Iyz,Izz] ])
    Iprin,Iaxes = linalg.eig(Itensor)
    if sort:
        s = Iprin.argsort()[::-1]
        Iprin = Iprin[s]
        Iaxes = Iaxes[:,s]
    if right_handed and not allclose(normalize(cross(Iaxes[:,0],Iaxes[:,1])),Iaxes[:,2]):
        Iaxes[:,2] = -Iaxes[:,2]
    return Iprin,Iaxes



# End

