sqaSymmetry.py

# Copyright 2009-2022 SecondQuantizationAlgebra Developers. All Rights Reserved.
#
# Licensed under the GNU General Public License v3.0;
# you may not use this file except in compliance with the License.
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.
#
# In addition, any modification or use of this software should
# cite the following paper:
#
#   E. Neuscamman, T. Yanai, and G. K.-L. Chan.
#   J. Chem. Phys. 130, 124102 (2009)
#
# Author: Eric Neuscamman <eric.neuscamman@gmail.com>
#
# The symmetry class represents a symmetry permutation of a tensor.
#
# The class consists of a permutation pattern and the constant factor
# that is produced when applying the permutation to the tensor's indices.
#
# The permutation, or pattern, for a tensor with n indices is represented
# by a tuple containing the integers 0 through n-1 in some order.
#
# The constant factor is either an int or a float.
#
# For example, the object created by symmetry((0,1,3,2), -1) implies that
# if you swap the tensor's last two indices, the result is equal to -1
# times the original tensor.

class symmetry:
    "A class representing symmetries in a tensor's indices"

    #------------------------------------------------------------------------------------------------

    def __init__(self,pattern,factor):
        patternError = False
        if type(pattern) != type((1,2)):
            patternError = True
        else:
            tempList = []
            for elem in pattern:
                if type(elem) != type(1):
                    patternError = True
                    break
                else:
                    tempList.append(elem)
            if not patternError:
                tempList.sort()
                patternError = ( tempList != range(len(pattern)) )
        if patternError:
            raise ValueError("pattern must be a tuple of contiguous, non-negative integers including zero. They need not be in order.")
        else:
            self.pattern = pattern
        if (factor == 1 or factor == -1) and type(factor) == type(1):
            self.factor = factor
        elif type(factor) == type(1) or type(factor) == type(1.0):
            self.factor = float(factor)
        else:
            raise TypeError("factor must be a float or an int.")

    #------------------------------------------------------------------------------------------------
    
    def __cmp__(self,other):
        if not isinstance(other,symmetry):
            raise TypeError("can only compare a symmetry object to other symmetry objects")
        return cmp(self.pattern,other.pattern)

    #------------------------------------------------------------------------------------------------
    
    def __str__(self):
        retval = str(self.pattern)
        retval += "%15.5e" %self.factor
        return retval

    #------------------------------------------------------------------------------------------------

    def copy(self):
        "Returns a copy of the symmetry"
        return symmetry(self.pattern, self.factor)

    #------------------------------------------------------------------------------------------------


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