Source code for cvxpy.atoms.affine.sum

"""
Copyright 2013 Steven Diamond

This file is part of CVXPY.

CVXPY 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.

CVXPY 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 CVXPY.  If not, see <http://www.gnu.org/licenses/>.
"""

from cvxpy.atoms.affine.affine_atom import AffAtom
from cvxpy.atoms.axis_atom import AxisAtom
import cvxpy.lin_ops.lin_utils as lu
import cvxpy.interface as intf
import numpy as np
from functools import wraps


class Sum(AxisAtom, AffAtom):
    """Sum the entries of an expression.

    Parameters
    ----------
    expr : Expression
        The expression to sum the entries of.
    axis : int
        The axis along which to sum.
    keepdims : bool
        Whether to drop dimensions after summing.
    """

    def __init__(self, expr, axis=None, keepdims=False):
        super(Sum, self).__init__(expr, axis=axis, keepdims=keepdims)

    def numeric(self, values):
        """Sums the entries of value.
        """
        if intf.is_sparse(values[0]):
            result = np.sum(values[0], axis=self.axis)
            if not self.keepdims and self.axis is not None:
                result = result.A.flatten()
        else:
            result = np.sum(values[0], axis=self.axis, keepdims=self.keepdims)
        return result

    @staticmethod
    def graph_implementation(arg_objs, shape, data=None):
        """Sum the linear expression's entries.

        Parameters
        ----------
        arg_objs : list
            LinExpr for each argument.
        shape : tuple
            The shape of the resulting expression.
        data :
            Additional data required by the atom.

        Returns
        -------
        tuple
            (LinOp for objective, list of constraints)
        """
        axis = data[0]
        keepdims = data[1]
        if axis is None:
            obj = lu.sum_entries(arg_objs[0], shape=shape)
        elif axis == 1:
            if keepdims:
                const_shape = (arg_objs[0].shape[1], 1)
            else:
                const_shape = (arg_objs[0].shape[1],)
            ones = lu.create_const(np.ones(const_shape), const_shape)
            obj = lu.rmul_expr(arg_objs[0], ones, shape)
        else:  # axis == 0
            if keepdims:
                const_shape = (1, arg_objs[0].shape[0])
            else:
                const_shape = (arg_objs[0].shape[0],)
            ones = lu.create_const(np.ones(const_shape), const_shape)
            obj = lu.mul_expr(ones, arg_objs[0], shape)

        return (obj, [])


[docs]@wraps(Sum) def sum(expr, axis=None, keepdims=False): """Wrapper for Sum class. """ if isinstance(expr, list): return __builtins__['sum'](expr) else: return Sum(expr, axis, keepdims)