4x4 inverse:

* change block selection threshold from 1e-2 to 1e-1
* add rigorous precision test

1 files changed, 5 insertions, 2 deletions

diff --git a/Eigen/src/LU/Inverse.h b/Eigen/src/LU/Inverse.h
index 306b5f60a..9d5e86845 100644
--- a/Eigen/src/LU/Inverse.h
+++ b/Eigen/src/LU/Inverse.h
@@ -235,8 +235,11 @@ struct ei_compute_inverse<MatrixType, ResultType, 4>
     int good_row0, good_row1, good_i;
     Matrix<RealScalar,6,1> absdet;
 
-    // any 2x2 block with determinant above this threshold will be considered good enough
-    RealScalar d = (matrix.col(0).squaredNorm()+matrix.col(1).squaredNorm()) * RealScalar(1e-2);
+    // any 2x2 block with determinant above this threshold will be considered good enough.
+    // The magic value 1e-1 here comes from experimentation. The bigger it is, the higher the precision,
+    // the slower the computation. This value 1e-1 gives precision almost as good as the brutal cofactors
+    // algorithm, both in average and in worst-case precision.
+    RealScalar d = (matrix.col(0).squaredNorm()+matrix.col(1).squaredNorm()) * RealScalar(1e-1);
     #define ei_inv_size4_helper_macro(i,row0,row1) \
     absdet[i] = ei_abs(matrix.coeff(row0,0)*matrix.coeff(row1,1) \
                                  - matrix.coeff(row0,1)*matrix.coeff(row1,0)); \