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Inverting a 4x4 matrix with try_inverse_mut doesn't leave self unchanged if the inversion fails. #1384

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merged 8 commits into from
May 5, 2024
Merged

Inverting a 4x4 matrix with try_inverse_mut doesn't leave self unchanged if the inversion fails. #1384

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d331bbd
inversion
jnyfah Apr 19, 2024
a0da49f
early return
jnyfah Apr 22, 2024
c21df4e
remove else
jnyfah Apr 22, 2024
5e87799
missed one cofactor
jnyfah Apr 28, 2024
825d078
add tests
jnyfah Apr 30, 2024
e3a08c9
test with a fixed input
jnyfah May 2, 2024
914a7cf
add assert
jnyfah May 2, 2024
343eb21
format
jnyfah May 5, 2024
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73 changes: 40 additions & 33 deletions src/linalg/inverse.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -145,13 +145,44 @@ where
{
let m = m.as_slice();

out[(0, 0)] = m[5].clone() * m[10].clone() * m[15].clone()
let cofactor00 = m[5].clone() * m[10].clone() * m[15].clone()
- m[5].clone() * m[11].clone() * m[14].clone()
- m[9].clone() * m[6].clone() * m[15].clone()
+ m[9].clone() * m[7].clone() * m[14].clone()
+ m[13].clone() * m[6].clone() * m[11].clone()
- m[13].clone() * m[7].clone() * m[10].clone();

let cofactor01 = -m[4].clone() * m[10].clone() * m[15].clone()
+ m[4].clone() * m[11].clone() * m[14].clone()
+ m[8].clone() * m[6].clone() * m[15].clone()
- m[8].clone() * m[7].clone() * m[14].clone()
- m[12].clone() * m[6].clone() * m[11].clone()
+ m[12].clone() * m[7].clone() * m[10].clone();

let cofactor02 = m[4].clone() * m[9].clone() * m[15].clone()
- m[4].clone() * m[11].clone() * m[13].clone()
- m[8].clone() * m[5].clone() * m[15].clone()
+ m[8].clone() * m[7].clone() * m[13].clone()
+ m[12].clone() * m[5].clone() * m[11].clone()
- m[12].clone() * m[7].clone() * m[9].clone();

let cofactor03 = -m[4].clone() * m[9].clone() * m[14].clone()
+ m[4].clone() * m[10].clone() * m[13].clone()
+ m[8].clone() * m[5].clone() * m[14].clone()
- m[8].clone() * m[6].clone() * m[13].clone()
- m[12].clone() * m[5].clone() * m[10].clone()
+ m[12].clone() * m[6].clone() * m[9].clone();

let det = m[0].clone() * cofactor00.clone()
+ m[1].clone() * cofactor01.clone()
+ m[2].clone() * cofactor02.clone()
+ m[3].clone() * cofactor03.clone();

if det.is_zero() {
return false;
}
out[(0, 0)] = cofactor00;

out[(1, 0)] = -m[1].clone() * m[10].clone() * m[15].clone()
+ m[1].clone() * m[11].clone() * m[14].clone()
+ m[9].clone() * m[2].clone() * m[15].clone()
Expand All @@ -173,12 +204,7 @@ where
- m[9].clone() * m[2].clone() * m[7].clone()
+ m[9].clone() * m[3].clone() * m[6].clone();

out[(0, 1)] = -m[4].clone() * m[10].clone() * m[15].clone()
+ m[4].clone() * m[11].clone() * m[14].clone()
+ m[8].clone() * m[6].clone() * m[15].clone()
- m[8].clone() * m[7].clone() * m[14].clone()
- m[12].clone() * m[6].clone() * m[11].clone()
+ m[12].clone() * m[7].clone() * m[10].clone();
out[(0, 1)] = cofactor01;

out[(1, 1)] = m[0].clone() * m[10].clone() * m[15].clone()
- m[0].clone() * m[11].clone() * m[14].clone()
Expand All @@ -201,12 +227,7 @@ where
+ m[8].clone() * m[2].clone() * m[7].clone()
- m[8].clone() * m[3].clone() * m[6].clone();

out[(0, 2)] = m[4].clone() * m[9].clone() * m[15].clone()
- m[4].clone() * m[11].clone() * m[13].clone()
- m[8].clone() * m[5].clone() * m[15].clone()
+ m[8].clone() * m[7].clone() * m[13].clone()
+ m[12].clone() * m[5].clone() * m[11].clone()
- m[12].clone() * m[7].clone() * m[9].clone();
out[(0, 2)] = cofactor02;

out[(1, 2)] = -m[0].clone() * m[9].clone() * m[15].clone()
+ m[0].clone() * m[11].clone() * m[13].clone()
Expand All @@ -222,12 +243,7 @@ where
+ m[12].clone() * m[1].clone() * m[7].clone()
- m[12].clone() * m[3].clone() * m[5].clone();

out[(0, 3)] = -m[4].clone() * m[9].clone() * m[14].clone()
+ m[4].clone() * m[10].clone() * m[13].clone()
+ m[8].clone() * m[5].clone() * m[14].clone()
- m[8].clone() * m[6].clone() * m[13].clone()
- m[12].clone() * m[5].clone() * m[10].clone()
+ m[12].clone() * m[6].clone() * m[9].clone();
out[(0, 3)] = cofactor03;

out[(3, 2)] = -m[0].clone() * m[5].clone() * m[11].clone()
+ m[0].clone() * m[7].clone() * m[9].clone()
Expand Down Expand Up @@ -257,21 +273,12 @@ where
+ m[8].clone() * m[1].clone() * m[6].clone()
- m[8].clone() * m[2].clone() * m[5].clone();

let det = m[0].clone() * out[(0, 0)].clone()
+ m[1].clone() * out[(0, 1)].clone()
+ m[2].clone() * out[(0, 2)].clone()
+ m[3].clone() * out[(0, 3)].clone();
let inv_det = T::one() / det;

if !det.is_zero() {
let inv_det = T::one() / det;

for j in 0..4 {
for i in 0..4 {
out[(i, j)] *= inv_det.clone();
}
for j in 0..4 {
for i in 0..4 {
out[(i, j)] *= inv_det.clone();
}
true
} else {
false
}
true
}
14 changes: 14 additions & 0 deletions tests/core/matrix.rs
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Expand Up @@ -1263,6 +1263,20 @@ fn column_iterator_double_ended_mut() {
assert_eq!(col_iter_mut.next(), None);
}

#[test]
fn test_inversion_failure_leaves_matrix_unchanged() {
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Maybe rename to _matrix4_unchanged to indicate that this was specifically an issue with 4x4 inversion and what we're testing here

let mut mat = na::Matrix4::new(
1.0, 2.0, 3.0, 4.0,
2.0, 4.0, 6.0, 8.0,
3.0, 6.0, 9.0, 12.0,
4.0, 8.0, 12.0, 16.0
);
let expected = mat.clone();
if !mat.try_inverse_mut() {
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This test is currently very brittle. Imagine that some change in an implementation detail somewhere caused mat.determinant() to return something not exactly 0.0. Then mat.try_inverse_mut() might return true and the test would succeed, although it's no longer testing what we want to test it.

Perhaps replace the if by an assert? E.g. assert!(!mat.try_inverse_mut()) followed by the assert_eq that you already have.

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@Andlon fixed it

assert_eq!(mat, expected);
}
}

#[test]
#[cfg(feature = "rayon")]
fn parallel_column_iteration() {
Expand Down
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