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This file is part of MADNESS.
Copyright (C) 2007,2010 Oak Ridge National Laboratory
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 2 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, write to the Free Software
Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
For more information please contact:
Robert J. Harrison
Oak Ridge National Laboratory
One Bethel Valley Road
P.O. Box 2008, MS-6367
email: harrisonrj@ornl.gov
tel: 865-241-3937
fax: 865-572-0680
$Id$
*/
/// \file slice.h
/// \brief Declares and implements Slice
/// \ingroup tensor
#ifndef MADNESS_TENSOR_SLICE_H__INCLUDED
#define MADNESS_TENSOR_SLICE_H__INCLUDED
#include <madness/tensor/vector_factory.h>
namespace madness {
/*!
\brief A slice defines a sub-range or patch of a dimension.
\ingroup tensor
\par Introduction
The slice \c Slice(start,end,step) defines the subvector
\code
[start, start+step, start+2*step, ..., end]
\endcode
with indices as if generated from these loops
\code
if (step > 0)
for (i=start; i<=end; i+=step) i;
else if (step < 0)
for (i=start; i>=end; i+=step) i;
else if (step == 0 && start == end)
defines a scalar
else
runtime error detected when slice is used
\endcode
Note that \c start and \c end are \em inclusive, unlike the Python
convention of specifying end+1 (note that we \em cannot do
this easily in C/C++ unless we also define a special value
to indicate the end of a dimension of unknown size).
\par Special meanings and conventions
Negative values for \c start or \c end (similar to Python)
are relative to the end of the (possibly unknown) dimension.
E.g.,
- \c end=-1 is equivalent to \c end=dim-1
- \c start=-4 is equivalent to \c start=dim-4
- \c step=0 and \c start==end implies dimension will be eliminated
when the slice is used to index a tensor
- The default constructor specifies the entire dimension
- If the input length is not an exact multiple of step, end is
rounded towards start to recover the behaviour of the
\c <= or \c >= bounds in the loops specified above.
Special slices have been defined as constants
- \c _ (1 underscore) = \c Slice(0,-1,1) = full slice in current order
- \c ___ (3 underscores) = Array of Slices with value \c _ so that \c t(___)
will generate an assignable view of the entire tensor \c t .
- _reverse = \c Slice(-1,0,-1) = full dimension reversed
\par Examples
- \c Slice() --- full slice in current order
- \c Slice(0,-1,1) --- full slice in current order
- \c Slice(3,3,0) --- eliminate this dimension setting index=3 (step=0)
- \c Slice(3,3,1) --- reduce a dimension to length 1 using index=3 (step=1)
- \c Slice(-1,0,-1) --- reverse a dimension
- \c Slice(0,-1,2) --- use all even numbered elements
- \c Slice(1,-1,2) --- use all odd numbered elements
*/
class Slice {
public:
long start;
long end;
long step;
inline Slice() : start(0), end(-1), step(1) {};
inline Slice(long s, long e, long stp=1) : start(s), end(e), step(stp) {};
inline Slice& operator=(const Slice& s) {
start=s.start;
end=s.end;
step=s.step;
return *this;
};
};
std::ostream& operator<<(std::ostream& stream, const Slice& s);
static const Slice _(0,-1,1); /// Entire dimension
static const std::vector<Slice> ___ = vector_factory(_,_,_,_,_,_); /// Entire tensor
static const Slice _reverse(-1,0,-1); /// Reversed dimension
}
#endif // MADNESS_TENSOR_SLICE_H__INCLUDED
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