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/* Copyright (c) 2008-2025 the MRtrix3 contributors.
*
* This Source Code Form is subject to the terms of the Mozilla Public
* License, v. 2.0. If a copy of the MPL was not distributed with this
* file, You can obtain one at http://mozilla.org/MPL/2.0/.
*
* Covered Software is provided under this License on an "as is"
* basis, without warranty of any kind, either expressed, implied, or
* statutory, including, without limitation, warranties that the
* Covered Software is free of defects, merchantable, fit for a
* particular purpose or non-infringing.
* See the Mozilla Public License v. 2.0 for more details.
*
* For more details, see http://www.mrtrix.org/.
*/
#include "command.h"
#include "progressbar.h"
#include "math/rng.h"
#include "thread.h"
#include "dwi/directions/file.h"
constexpr size_t default_permutations = 1e8;
using namespace MR;
using namespace App;
void usage ()
{
AUTHOR = "J-Donald Tournier (jdtournier@gmail.com)";
SYNOPSIS = "Split a set of evenly distributed directions (as generated "
"by dirgen) into approximately uniformly distributed subsets";
ARGUMENTS
+ Argument ("dirs", "the text file containing the directions.").type_file_in()
+ Argument ("out", "the output partitioned directions").type_file_out().allow_multiple();
OPTIONS
+ Option ("permutations", "number of permutations to try (default: " + str(default_permutations) + ")")
+ Argument ("num").type_integer (1)
+ Option ("cartesian", "Output the directions in Cartesian coordinates [x y z] instead of [az el].");
}
using value_type = double;
using vector3_type = Eigen::Vector3d;
class Shared { MEMALIGN(Shared)
public:
Shared (const Eigen::MatrixXd& directions, size_t num_subsets, size_t target_num_permutations) :
directions (directions), subset (num_subsets),
best_energy (std::numeric_limits<value_type>::max()),
target_num_permutations (target_num_permutations),
num_permutations (0) {
size_t s = 0;
for (ssize_t n = 0; n < directions.rows(); ++n) {
subset[s++].push_back (n);
if (s >= num_subsets) s = 0;
}
INFO ("split " + str(directions.rows()) + " directions into subsets with " +
str([&]{ vector<size_t> c; for (auto& x : subset) c.push_back (x.size()); return c; }()) + " volumes");
}
bool update (value_type energy, const vector<vector<size_t>>& set)
{
std::lock_guard<std::mutex> lock (mutex);
if (!progress) progress.reset (new ProgressBar ("distributing directions", target_num_permutations));
if (energy < best_energy) {
best_energy = energy;
best_subset = set;
progress->set_text ("distributing directions (current best configuration: energy = " + str(best_energy) + ")");
}
++num_permutations;
++(*progress);
return num_permutations < target_num_permutations;
}
value_type energy (size_t i, size_t j) const {
vector3_type a = { directions(i,0), directions(i,1), directions(i,2) };
vector3_type b = { directions(j,0), directions(j,1), directions(j,2) };
return 1.0 / (a-b).norm() + 1.0 / (a+b).norm();
}
const vector<vector<size_t>>& get_init_subset () const { return subset; }
const vector<vector<size_t>>& get_best_subset () const { return best_subset; }
protected:
const Eigen::MatrixXd& directions;
std::mutex mutex;
vector<vector<size_t>> subset, best_subset;
value_type best_energy;
const size_t target_num_permutations;
size_t num_permutations;
std::unique_ptr<ProgressBar> progress;
};
class EnergyCalculator { MEMALIGN(EnergyCalculator)
public:
EnergyCalculator (Shared& shared) : shared (shared), subset (shared.get_init_subset()) { }
void execute () {
while (eval());
}
void next_permutation ()
{
size_t i,j;
std::uniform_int_distribution<size_t> dist(0, subset.size()-1);
do {
i = dist (rng);
j = dist (rng);
} while (i == j);
size_t n_i = std::uniform_int_distribution<size_t> (0, subset[i].size()-1) (rng);
size_t n_j = std::uniform_int_distribution<size_t> (0, subset[j].size()-1) (rng);
std::swap (subset[i][n_i], subset[j][n_j]);
}
bool eval ()
{
next_permutation();
value_type energy = 0.0;
for (auto& s: subset) {
value_type current_energy = 0.0;
for (size_t i = 0; i < s.size(); ++i)
for (size_t j = i+1; j < s.size(); ++j)
current_energy += shared.energy (s[i], s[j]);
energy = std::max (energy, current_energy);
}
return shared.update (energy, subset);
}
protected:
Shared& shared;
vector<vector<size_t>> subset;
Math::RNG rng;
};
void run ()
{
auto directions = DWI::Directions::load_cartesian (argument[0]);
const size_t num_subsets = argument.size() - 1;
if (num_subsets == 1)
throw Exception ("Directions must be split across two or more output files");
const size_t num_permutations = get_option_value<size_t> ("permutations", default_permutations);
vector<vector<size_t>> best;
{
Shared shared (directions, num_subsets, num_permutations);
Thread::run (Thread::multi (EnergyCalculator (shared)), "energy eval thread");
best = shared.get_best_subset();
}
const bool cartesian = get_options("cartesian").size();
for (size_t i = 0; i < best.size(); ++i) {
Eigen::MatrixXd output (best[i].size(), 3);
for (size_t n = 0; n < best[i].size(); ++n)
output.row(n) = directions.row (best[i][n]);
DWI::Directions::save (output, argument[i+1], cartesian);
}
}
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