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37 * Implements density similarity measures and their derivatives.
39 * \author Christian Blau <blau@kth.se>
40 * \ingroup module_math
44 #include "densityfit.h"
49 #include "gromacs/math/multidimarray.h"
50 #include "gromacs/math/vec.h"
51 #include "gromacs/utility/exceptions.h"
56 class DensitySimilarityMeasureImpl
59 virtual ~DensitySimilarityMeasureImpl();
60 //! convenience typedef
61 using density = DensitySimilarityMeasure::density;
62 //! \copydoc DensitySimilarityMeasure::gradient(DensitySimilarityMeasure::density comparedDensity)
63 virtual density gradient(density comparedDensity) = 0;
64 //! \copydoc DensitySimilarityMeasure::similarity(density comparedDensity)
65 virtual real similarity(density comparedDensity) = 0;
66 //! clone to allow copy operations
67 virtual std::unique_ptr<DensitySimilarityMeasureImpl> clone() = 0;
69 DensitySimilarityMeasureImpl::~DensitySimilarityMeasureImpl() = default;
74 /****************** Inner Product *********************************************/
77 * \brief Implementation for DensitySimilarityInnerProduct.
79 * The similarity measure itself is documented in DensitySimilarityMeasureMethod::innerProduct.
81 class DensitySimilarityInnerProduct final : public DensitySimilarityMeasureImpl
84 //! Construct similarity measure by setting the reference density
85 DensitySimilarityInnerProduct(density referenceDensity);
86 //! The gradient for the inner product similarity measure is the reference density divided by the number of voxels
87 density gradient(density comparedDensity) override;
89 std::unique_ptr<DensitySimilarityMeasureImpl> clone() override;
90 //! The similarity between reference density and compared density
91 real similarity(density comparedDensity) override;
94 //! A view on the reference density
95 const density referenceDensity_;
96 //! Stores the gradient of the similarity measure in memory
97 MultiDimArray<std::vector<float>, dynamicExtents3D> gradient_;
100 DensitySimilarityInnerProduct::DensitySimilarityInnerProduct(density referenceDensity) :
101 referenceDensity_{ referenceDensity },
102 gradient_{ referenceDensity.extents() }
104 const auto numVoxels = gradient_.asConstView().mapping().required_span_size();
105 /* the gradient for the inner product measure of fit is constant and does not
106 * depend on the compared density, so it is pre-computed here */
107 std::transform(begin(referenceDensity_), end(referenceDensity), begin(gradient_), [numVoxels](float x) {
108 return x / numVoxels;
112 real DensitySimilarityInnerProduct::similarity(density comparedDensity)
114 if (comparedDensity.extents() != referenceDensity_.extents())
116 GMX_THROW(RangeError("Reference density and compared density need to have same extents."));
118 /* the similarity measure uses the gradient instead of the reference,
119 * here, because it is the reference density divided by the number of voxels */
120 return std::inner_product(begin(gradient_), end(gradient_), begin(comparedDensity), 0.);
123 DensitySimilarityMeasure::density DensitySimilarityInnerProduct::gradient(density comparedDensity)
125 /* even though the gradient density does not depend on the compad density,
126 * still checking the extents to make sure we're consistent */
127 if (comparedDensity.extents() != referenceDensity_.extents())
129 GMX_THROW(RangeError("Reference density and compared density need to have same extents."));
132 return gradient_.asConstView();
135 std::unique_ptr<DensitySimilarityMeasureImpl> DensitySimilarityInnerProduct::clone()
137 return std::make_unique<DensitySimilarityInnerProduct>(referenceDensity_);
140 /****************** Relative Entropy *****************************************/
142 //! Calculate a single summand in the relative entropy sum.
143 real relativeEntropyAtVoxel(real reference, real comparison)
145 if ((reference > 0) && (comparison > 0))
147 return reference * (std::log(comparison / reference));
152 //! Calculate a single relative entropy gradient entry at a voxel.
153 real relativeEntropyGradientAtVoxel(real reference, real comparison)
155 if ((reference > 0) && (comparison > 0))
157 return reference / comparison;
163 * \brief Implementation for DensitySimilarityRelativeEntropy.
165 * The similarity measure itself is documented in DensitySimilarityMeasureMethod::RelativeEntropy.
167 class DensitySimilarityRelativeEntropy final : public DensitySimilarityMeasureImpl
170 //! Construct similarity measure by setting the reference density
171 DensitySimilarityRelativeEntropy(density referenceDensity);
172 //! The gradient for the relative entropy similarity measure
173 density gradient(density comparedDensity) override;
175 std::unique_ptr<DensitySimilarityMeasureImpl> clone() override;
176 //! The similarity between reference density and compared density
177 real similarity(density comparedDensity) override;
180 //! A view on the reference density
181 const density referenceDensity_;
182 //! Stores the gradient of the similarity measure in memory
183 MultiDimArray<std::vector<float>, dynamicExtents3D> gradient_;
186 DensitySimilarityRelativeEntropy::DensitySimilarityRelativeEntropy(density referenceDensity) :
187 referenceDensity_{ referenceDensity },
188 gradient_(referenceDensity.extents())
192 real DensitySimilarityRelativeEntropy::similarity(density comparedDensity)
194 if (comparedDensity.extents() != referenceDensity_.extents())
196 GMX_THROW(RangeError("Reference density and compared density need to have same extents."));
198 return std::inner_product(begin(referenceDensity_),
199 end(referenceDensity_),
200 begin(comparedDensity),
203 relativeEntropyAtVoxel);
206 DensitySimilarityMeasure::density DensitySimilarityRelativeEntropy::gradient(density comparedDensity)
208 if (comparedDensity.extents() != referenceDensity_.extents())
210 GMX_THROW(RangeError("Reference density and compared density need to have same extents."));
212 std::transform(begin(referenceDensity_),
213 end(referenceDensity_),
214 begin(comparedDensity),
216 relativeEntropyGradientAtVoxel);
217 return gradient_.asConstView();
220 std::unique_ptr<DensitySimilarityMeasureImpl> DensitySimilarityRelativeEntropy::clone()
222 return std::make_unique<DensitySimilarityRelativeEntropy>(referenceDensity_);
225 /****************** Cross Correlation *****************************************/
227 //! Helper values for evaluating the cross correlation
228 struct CrossCorrelationEvaluationHelperValues
230 //! The mean of the reference density
231 real meanReference = 0;
232 //! The mean of the compared density
233 real meanComparison = 0;
234 //! The sum of the squared reference density voxel values
235 real referenceSquaredSum = 0;
236 //! The sum of the squared compared density voxel values
237 real comparisonSquaredSum = 0;
238 //! The covariance of the refernce and the compared density
242 /*! \brief Calculate helper values for the cross-correlation.
244 * Enables numerically stable single-pass cross-correlation evaluation algorithm
245 * as described in Bennett, J., Grout, R. , Pebay, P., Roe D., Thompson D.
246 * "Numerically Stable, Single-Pass, Parallel Statistics Algorithms"
247 * and implemented in boost's correlation coefficient
249 CrossCorrelationEvaluationHelperValues evaluateHelperValues(DensitySimilarityMeasure::density reference,
250 DensitySimilarityMeasure::density compared)
252 CrossCorrelationEvaluationHelperValues helperValues;
256 auto referenceIterator = begin(reference);
257 for (const real comp : compared)
259 const real refHelper = *referenceIterator - helperValues.meanReference;
260 const real comparisonHelper = comp - helperValues.meanComparison;
261 helperValues.referenceSquaredSum += (i * square(refHelper)) / (i + 1);
262 helperValues.comparisonSquaredSum += (i * square(comparisonHelper)) / (i + 1);
263 helperValues.covariance += i * refHelper * comparisonHelper / (i + 1);
264 helperValues.meanReference += refHelper / (i + 1);
265 helperValues.meanComparison += comparisonHelper / (i + 1);
274 //! Calculate a single cross correlation gradient entry at a voxel.
275 class CrossCorrelationGradientAtVoxel
278 //! Set up the gradident calculation with pre-computed values
279 CrossCorrelationGradientAtVoxel(const CrossCorrelationEvaluationHelperValues& preComputed) :
280 prefactor_(evaluatePrefactor(preComputed.comparisonSquaredSum, preComputed.referenceSquaredSum)),
281 comparisonPrefactor_(preComputed.covariance / preComputed.comparisonSquaredSum),
282 meanReference_(preComputed.meanReference),
283 meanComparison_(preComputed.meanComparison)
286 //! Evaluate the cross correlation gradient at a voxel
287 real operator()(real reference, real comparison)
290 * (reference - meanReference_ - comparisonPrefactor_ * (comparison - meanComparison_));
294 static real evaluatePrefactor(real comparisonSquaredSum, real referenceSquaredSum)
296 GMX_ASSERT(comparisonSquaredSum > 0,
297 "Squared sum of comparison values needs to be larger than zero.");
298 GMX_ASSERT(referenceSquaredSum > 0,
299 "Squared sum of reference values needs to be larger than zero.");
300 return 1.0 / (sqrt(comparisonSquaredSum) * sqrt(referenceSquaredSum));
302 const real prefactor_;
303 const real comparisonPrefactor_;
304 const real meanReference_;
305 const real meanComparison_;
309 * \brief Implementation for DensitySimilarityCrossCorrelation.
311 * The similarity measure itself is documented in DensitySimilarityMeasureMethod::crossCorrelation.
313 class DensitySimilarityCrossCorrelation final : public DensitySimilarityMeasureImpl
316 //! Construct similarity measure by setting the reference density
317 DensitySimilarityCrossCorrelation(density referenceDensity);
318 //! The gradient for the cross correlation similarity measure
319 density gradient(density comparedDensity) override;
321 std::unique_ptr<DensitySimilarityMeasureImpl> clone() override;
322 //! The similarity between reference density and compared density
323 real similarity(density comparedDensity) override;
326 //! A view on the reference density
327 const density referenceDensity_;
328 //! Stores the gradient of the similarity measure in memory
329 MultiDimArray<std::vector<float>, dynamicExtents3D> gradient_;
332 DensitySimilarityCrossCorrelation::DensitySimilarityCrossCorrelation(density referenceDensity) :
333 referenceDensity_{ referenceDensity },
334 gradient_(referenceDensity.extents())
338 real DensitySimilarityCrossCorrelation::similarity(density comparedDensity)
340 if (comparedDensity.extents() != referenceDensity_.extents())
342 GMX_THROW(RangeError("Reference density and compared density need to have same extents."));
345 CrossCorrelationEvaluationHelperValues helperValues =
346 evaluateHelperValues(referenceDensity_, comparedDensity);
348 if ((helperValues.referenceSquaredSum == 0) || (helperValues.comparisonSquaredSum == 0))
353 // To avoid numerical instability due to large squared density value sums
354 // division is re-written to avoid multiplying two large numbers
355 // as product of two seperate divisions of smaller numbers
356 const real covarianceSqrt = sqrt(fabs(helperValues.covariance));
357 const int sign = helperValues.covariance > 0 ? 1 : -1;
358 return sign * (covarianceSqrt / sqrt(helperValues.referenceSquaredSum))
359 * (covarianceSqrt / sqrt(helperValues.comparisonSquaredSum));
362 DensitySimilarityMeasure::density DensitySimilarityCrossCorrelation::gradient(density comparedDensity)
364 if (comparedDensity.extents() != referenceDensity_.extents())
366 GMX_THROW(RangeError("Reference density and compared density need to have same extents."));
369 CrossCorrelationEvaluationHelperValues helperValues =
370 evaluateHelperValues(referenceDensity_, comparedDensity);
372 std::transform(begin(referenceDensity_),
373 end(referenceDensity_),
374 begin(comparedDensity),
376 CrossCorrelationGradientAtVoxel(helperValues));
378 return gradient_.asConstView();
381 std::unique_ptr<DensitySimilarityMeasureImpl> DensitySimilarityCrossCorrelation::clone()
383 return std::make_unique<DensitySimilarityCrossCorrelation>(referenceDensity_);
390 DensitySimilarityMeasure::DensitySimilarityMeasure(DensitySimilarityMeasureMethod method,
391 density referenceDensity)
393 // chose the implementation depending on the method of density comparison
394 // throw an error if the method is not known
397 case DensitySimilarityMeasureMethod::innerProduct:
398 impl_ = std::make_unique<DensitySimilarityInnerProduct>(referenceDensity);
400 case DensitySimilarityMeasureMethod::relativeEntropy:
401 impl_ = std::make_unique<DensitySimilarityRelativeEntropy>(referenceDensity);
403 case DensitySimilarityMeasureMethod::crossCorrelation:
404 impl_ = std::make_unique<DensitySimilarityCrossCorrelation>(referenceDensity);
406 default: GMX_THROW(NotImplementedError("Similarity measure not implemented."));
410 DensitySimilarityMeasure::density DensitySimilarityMeasure::gradient(density comparedDensity)
412 return impl_->gradient(comparedDensity);
415 real DensitySimilarityMeasure::similarity(density comparedDensity)
417 return impl_->similarity(comparedDensity);
420 DensitySimilarityMeasure::~DensitySimilarityMeasure() = default;
422 DensitySimilarityMeasure::DensitySimilarityMeasure(const DensitySimilarityMeasure& other) :
423 impl_(other.impl_->clone())
427 DensitySimilarityMeasure& DensitySimilarityMeasure::operator=(const DensitySimilarityMeasure& other)
429 impl_ = other.impl_->clone();
433 DensitySimilarityMeasure::DensitySimilarityMeasure(DensitySimilarityMeasure&&) noexcept = default;
435 DensitySimilarityMeasure& DensitySimilarityMeasure::operator=(DensitySimilarityMeasure&&) noexcept = default;