madness::Slice Class Reference

A slice defines a sub-range or patch of a dimension. More...

#include <slice.h>

Public Member Functions
	Slice ()
	Slice (const Slice &)=default
	Slice (long s, long e, long stp=1)
Slice &	operator= (const Slice &)=default
template<typename Archive >
void	serialize (Archive &ar)

Public Attributes
long	end
long	start
long	step

Detailed Description

A slice defines a sub-range or patch of a dimension.

Introduction

The slice Slice(start,end,step) defines the subvector

[start, start+step, start+2*step, ..., end]

with indices as if generated from these loops

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

Note that start and end are inclusive, unlike the Python convention of specifying end+1 (note that we cannot do this easily in C/C++ unless we also define a special value to indicate the end of a dimension of unknown size).

Special meanings and conventions

Negative values for start or end (similar to Python) are relative to the end of the (possibly unknown) dimension. E.g.,

• end=-1 is equivalent to end=dim-1
• start=-4 is equivalent to start=dim-4
• step=0 and 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 <= or >= bounds in the loops specified above.

Special slices have been defined as constants

• _ (1 underscore) = Slice(0,-1,1) = full slice in current order
• ___ (3 underscores) = Array of Slices with value _ so that t(___) will generate an assignable view of the entire tensor t .
• _reverse = Slice(-1,0,-1) = full dimension reversed

Examples

• Slice() — full slice in current order
• Slice(0,-1,1) — full slice in current order
• Slice(3,3,0) — eliminate this dimension setting index=3 (step=0)
• Slice(3,3,1) — reduce a dimension to length 1 using index=3 (step=1)
• Slice(-1,0,-1) — reverse a dimension
• Slice(0,-1,2) — use all even numbered elements
• Slice(1,-1,2) — use all odd numbered elements

Constructor & Destructor Documentation

Slice() [1/3]

madness::Slice::Slice ( )

inline

Slice() [2/3]

madness::Slice::Slice ( long  s, long  e, long  stp = 1  )

inline

Slice() [3/3]

madness::Slice::Slice ( const Slice &  )

default

Member Function Documentation

operator=()

Slice & madness::Slice::operator= ( const Slice &  )

default

serialize()

template<typename Archive >

void madness::Slice::serialize ( Archive &  ar )

inline

References end, start, and step.

Member Data Documentation

end

long madness::Slice::end

Referenced by serialize().

start

long madness::Slice::start

Referenced by serialize().

step

long madness::Slice::step

Referenced by serialize().

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The documentation for this class was generated from the following file:

• slice.h