Speedup corrector.cc
Add a specialization for the common case where the residual block
outputs exactly one residual.
The matrix routines used by Corrector can be then specialized to
a scalar and be made considerably faster.
For denoising upto 400% speedup is observed.
Change-Id: I8e3f24b8ba41caa8e62ad97c5f5e96ab6ea47150
diff --git a/internal/ceres/corrector.cc b/internal/ceres/corrector.cc
index eff4dff..c3858ab 100644
--- a/internal/ceres/corrector.cc
+++ b/internal/ceres/corrector.cc
@@ -113,12 +113,19 @@
double* residuals, double* jacobian) {
DCHECK(residuals != NULL);
DCHECK(jacobian != NULL);
- ConstVectorRef r_ref(residuals, nrow);
- MatrixRef j_ref(jacobian, nrow, ncol);
- // Equation 11 in BANS.
- j_ref = sqrt_rho1_ * (j_ref - alpha_sq_norm_ *
- r_ref * (r_ref.transpose() * j_ref));
+ if (nrow == 1) {
+ // Specialization for the case where the residual is a scalar.
+ VectorRef j_ref(jacobian, ncol);
+ j_ref *= sqrt_rho1_ * (1.0 - alpha_sq_norm_ * pow(*residuals, 2));
+ } else {
+ ConstVectorRef r_ref(residuals, nrow);
+ MatrixRef j_ref(jacobian, nrow, ncol);
+
+ // Equation 11 in BANS.
+ j_ref = sqrt_rho1_ * (j_ref - alpha_sq_norm_ *
+ r_ref * (r_ref.transpose() * j_ref));
+ }
}
} // namespace internal
