coco
120 lines
3.6 KiB
C++
120 lines
3.6 KiB
C++
// Copyright (C) 2011 Davis E. King (davis@dlib.net)
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// License: Boost Software License See LICENSE.txt for the full license.
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#undef DLIB_PROJECTION_HASh_ABSTRACT_Hh_
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#ifdef DLIB_PROJECTION_HASh_ABSTRACT_Hh_
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#include "../matrix.h"
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namespace dlib
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{
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// ----------------------------------------------------------------------------------------
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class projection_hash
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{
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/*!
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WHAT THIS OBJECT REPRESENTS
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This is a tool for hashing elements of a vector space into the integers.
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It is intended to represent locality sensitive hashing functions such as
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the popular random projection hashing method.
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In particular, it represents hash functions of the form:
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hash bit 0 = sign(rowm(P*v + O,0))
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hash bit 1 = sign(rowm(P*v + O,1))
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hash bit 2 = sign(rowm(P*v + O,2))
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...
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Where v is the vector to be hashed. The parameters of the projection
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hash are the P and O matrices.
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THREAD SAFETY
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The const members of this object can be called concurrently from multiple
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threads, however, any operation that modifies the state of an instance of
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this object must serialize access to that instance.
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!*/
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public:
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projection_hash(
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);
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/*!
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ensures
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- #get_projection_matrix().size() == 0
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- #get_offset_matrix().size() == 0
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!*/
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template <typename EXP1, typename EXP2>
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projection_hash(
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const matrix_exp<EXP1>& proj,
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const matrix_exp<EXP2>& offset
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);
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/*!
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requires
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- proj.nr() == offset.nr()
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ensures
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- #get_projection_matrix() == proj
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- #get_offset_matrix() == offset
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!*/
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const matrix<double>& get_projection_matrix (
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) const;
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/*!
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ensures
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- returns the P matrix discussed above in the WHAT THIS OBJECT REPRESENTS
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section.
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!*/
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const matrix<double,0,1>& get_offset_matrix (
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) const;
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/*!
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ensures
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- returns the O matrix discussed above in the WHAT THIS OBJECT REPRESENTS
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section.
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!*/
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unsigned long num_hash_bins (
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) const;
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/*!
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ensures
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- returns the number of possible outputs from this hashing function.
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- Specifically, returns: std::pow(2, get_offset_matrix().size())
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!*/
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template <typename EXP>
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unsigned long operator() (
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const matrix_exp<EXP>& v
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) const;
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/*!
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requires
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- is_col_vector(v) == true
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- v.size() == get_projection_matrix().nc()
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- v.size() > 0
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ensures
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- hashes v into the range [0, num_hash_bins()) using the method
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discussed in the WHAT THIS OBJECT REPRESENTS section.
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!*/
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};
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// ----------------------------------------------------------------------------------------
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void serialize (
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const projection_hash& item,
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std::ostream& out
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);
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/*!
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provides serialization support
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!*/
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void deserialize (
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projection_hash& item,
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std::istream& in
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);
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/*!
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provides deserialization support
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!*/
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// ----------------------------------------------------------------------------------------
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}
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#endif // DLIB_PROJECTION_HASh_ABSTRACT_Hh_
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