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Simplify rectangular lattice crossing and correctly handle corner checks #3703

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Merged
GuySten merged 4 commits into from
Jan 6, 2026
Merged

Simplify rectangular lattice crossing and correctly handle corner checks #3703

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b25cf86
simplify and fix RectLattice distance calculation
GuySten Jan 1, 2026
ed3217d
add guards against divide by zero
GuySten Jan 5, 2026
568b4e1
Guard against zero in checks for lattice_trans
paulromano Jan 6, 2026
b82f8d8
Update lattice corner test
paulromano Jan 6, 2026
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47 changes: 12 additions & 35 deletions src/lattice.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -260,46 +260,23 @@ std::pair<double, array<int, 3>> RectLattice::distance(
// Determine the oncoming edge.
double x0 {copysign(0.5 * pitch_[0], u.x)};
double y0 {copysign(0.5 * pitch_[1], u.y)};
double z0;

// Left and right sides
double d {INFTY};
array<int, 3> lattice_trans;
if ((std::abs(x - x0) > FP_PRECISION) && u.x != 0) {
d = (x0 - x) / u.x;
if (u.x > 0) {
lattice_trans = {1, 0, 0};
} else {
lattice_trans = {-1, 0, 0};
}
double d = std::min((x0 - x) / u.x, (y0 - y) / u.y);
if (is_3d_) {
z0 = copysign(0.5 * pitch_[2], u.z);
d = std::min(d, (z0 - z) / u.z);
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}

// Front and back sides
if ((std::abs(y - y0) > FP_PRECISION) && u.y != 0) {
double this_d = (y0 - y) / u.y;
if (this_d < d) {
d = this_d;
if (u.y > 0) {
lattice_trans = {0, 1, 0};
} else {
lattice_trans = {0, -1, 0};
}
}
}
array<int, 3> lattice_trans = {0, 0, 0};

// Top and bottom sides
if (std::abs(x + u.x * d - x0) < FP_PRECISION)
lattice_trans[0] = copysign(1, u.x);
if (std::abs(y + u.y * d - y0) < FP_PRECISION)
lattice_trans[1] = copysign(1, u.y);
if (is_3d_) {
double z0 {copysign(0.5 * pitch_[2], u.z)};
if ((std::abs(z - z0) > FP_PRECISION) && u.z != 0) {
double this_d = (z0 - z) / u.z;
if (this_d < d) {
d = this_d;
if (u.z > 0) {
lattice_trans = {0, 0, 1};
} else {
lattice_trans = {0, 0, -1};
}
}
}
if (std::abs(z + u.z * d - z0) < FP_PRECISION)
lattice_trans[2] = copysign(1, u.z);
}

return {d, lattice_trans};
Expand Down
Empty file added tests/regression_tests/lattice_corner_crossing/__init__.py
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Empty file.
61 changes: 61 additions & 0 deletions tests/regression_tests/lattice_corner_crossing/inputs_true.dat
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Original file line number Diff line number Diff line change
@@ -0,0 +1,61 @@
<?xml version='1.0' encoding='utf-8'?>
<model>
<materials>
<material id="1" name="air">
<density value="0.001" units="g/cc"/>
<nuclide name="N14" ao="1.0"/>
</material>
<material id="2" name="metal">
<density value="7" units="g/cc"/>
<nuclide name="Fe56" ao="1.0"/>
</material>
</materials>
<geometry>
<cell id="1" name="outside_lattice" material="1" region="-5 (-1 | 2 | -3 | 4)" universe="1"/>
<cell id="2" name="inside_lattice" fill="4" region="1 -2 3 -4" universe="1"/>
<cell id="3" material="2" region="-6" universe="2"/>
<cell id="4" material="1" region="-7" universe="3"/>
<lattice id="4">
<pitch>10.0 10.0</pitch>
<dimension>2 2</dimension>
<lower_left>-10.0 -10.0</lower_left>
<universes>
2 3
3 2 </universes>
</lattice>
<surface id="1" name="left" type="x-plane" coeffs="-10.0"/>
<surface id="2" name="right" type="x-plane" coeffs="10.0"/>
<surface id="3" name="bottom" type="y-plane" coeffs="-10.0"/>
<surface id="4" name="top" type="y-plane" coeffs="10.0"/>
<surface id="5" type="z-cylinder" boundary="vacuum" coeffs="0 0 20.0"/>
<surface id="6" type="sphere" coeffs="0.0 0.0 0.0 1e+90"/>
<surface id="7" type="sphere" coeffs="0.0 0.0 0.0 1e+90"/>
</geometry>
<settings>
<run_mode>fixed source</run_mode>
<particles>1000</particles>
<batches>10</batches>
<max_lost_particles>100000000</max_lost_particles>
<source type="independent" strength="1.0" particle="neutron">
<space type="point">
<parameters>-0.7071067811865476 -0.7071067811865475 0.0</parameters>
</space>
<angle type="monodirectional" reference_uvw="0.7071067811865476 0.7071067811865475 0.0"/>
</source>
</settings>
<tallies>
<mesh id="1">
<dimension>10 10 1</dimension>
<lower_left>-20.0 -20.0 -1000000000.0</lower_left>
<upper_right>20.0 20.0 1000000000.0</upper_right>
</mesh>
<filter id="1" type="mesh">
<bins>1</bins>
</filter>
<tally id="1">
<filters>1</filters>
<scores>flux</scores>
<estimator>tracklength</estimator>
</tally>
</tallies>
</model>
201 changes: 201 additions & 0 deletions tests/regression_tests/lattice_corner_crossing/results_true.dat
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Original file line number Diff line number Diff line change
@@ -0,0 +1,201 @@
tally 1:
0.000000E+00
0.000000E+00
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0.000000E+00
2.648775E-03
7.016009E-06
0.000000E+00
0.000000E+00
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0.000000E+00
0.000000E+00
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2.981847E-03
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0.000000E+00
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4.388206E-03
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4.680753E-02
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0.000000E+00
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2.115487E-03
4.475286E-06
0.000000E+00
0.000000E+00
0.000000E+00
0.000000E+00
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