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Diffstat (limited to 'extern/ceres/internal/ceres/parallel_utils.cc')
| -rw-r--r-- | extern/ceres/internal/ceres/parallel_utils.cc | 90 |
1 files changed, 90 insertions, 0 deletions
diff --git a/extern/ceres/internal/ceres/parallel_utils.cc b/extern/ceres/internal/ceres/parallel_utils.cc new file mode 100644 index 00000000000..e1cb5f979ec --- /dev/null +++ b/extern/ceres/internal/ceres/parallel_utils.cc @@ -0,0 +1,90 @@ +// Ceres Solver - A fast non-linear least squares minimizer +// Copyright 2018 Google Inc. All rights reserved. +// http://ceres-solver.org/ +// +// Redistribution and use in source and binary forms, with or without +// modification, are permitted provided that the following conditions are met: +// +// * Redistributions of source code must retain the above copyright notice, +// this list of conditions and the following disclaimer. +// * Redistributions in binary form must reproduce the above copyright notice, +// this list of conditions and the following disclaimer in the documentation +// and/or other materials provided with the distribution. +// * Neither the name of Google Inc. nor the names of its contributors may be +// used to endorse or promote products derived from this software without +// specific prior written permission. +// +// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" +// AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE +// IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE +// ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE +// LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR +// CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF +// SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS +// INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN +// CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) +// ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE +// POSSIBILITY OF SUCH DAMAGE. +// +// Author: wjr@google.com (William Rucklidge) + +#include "ceres/parallel_utils.h" + +namespace ceres { +namespace internal { + +void LinearIndexToUpperTriangularIndex(int k, int n, int* i, int* j) { + // This works by unfolding a rectangle into a triangle. + // Say n is even. 4 is a nice even number. The 10 i,j pairs that we + // want to produce are: + // 0,0 0,1 0,2 0,3 + // 1,1 1,2 1,3 + // 2,2 2,3 + // 3,3 + // This triangle can be folded into a 5x2 rectangle: + // 3,3 0,0 0,1 0,2 0,3 + // 2,2 2,3 1,1 1,2 1,3 + + // If N is odd, say 5, then the 15 i,j pairs are: + // 0,0 0,1 0,2 0,3 0,4 + // 1,1 1,2 1,3 1,4 + // 2,2 2,3 2,3 + // 3,3 3,4 + // 4,4 + // which folds to a 5x3 rectangle: + // 0,0 0,1 0,2 0,3 0,4 + // 4,4 1,1 1,2 1,3 1,4 + // 3,3 3,4 2,2 2,3 2,4 + + // All this function does is map the linear iteration position to a + // location in the rectangle and work out the appropriate (i, j) for that + // location. + if (n & 1) { + // Odd n. The tip of the triangle is on row 1. + int w = n; // Width of the rectangle to unfold + int i0 = k / w; + int j0 = k % w; + if (j0 >= i0) { + *i = i0; + *j = j0; + } else { + *i = n - i0; + *j = *i + j0; + } + } else { + // Even n. The tip of the triangle is on row 0, making it one wider. + int w = n + 1; + int i0 = k / w; + int j0 = k % w; + if (j0 > i0) { + *i = i0; + *j = j0 - 1; + } else { + *i = n - 1 - i0; + *j = *i + j0; + } + } +} + +} // namespace internal +} // namespace ceres |