From f6fc122290ab1b34c84272c1843a1c56091ab876 Mon Sep 17 00:00:00 2001
From: Dmitri Naumov <github@naumov.de>
Date: Thu, 20 Oct 2016 00:10:43 +0200
Subject: [PATCH] [MaL] Speedup the piecewise interpolation.
---
.../PiecewiseLinearInterpolation.cpp | 41 +++++++++++--------
1 file changed, 25 insertions(+), 16 deletions(-)
diff --git a/MathLib/InterpolationAlgorithms/PiecewiseLinearInterpolation.cpp b/MathLib/InterpolationAlgorithms/PiecewiseLinearInterpolation.cpp
index cf984006af5..33ab8f3ddc8 100644
--- a/MathLib/InterpolationAlgorithms/PiecewiseLinearInterpolation.cpp
+++ b/MathLib/InterpolationAlgorithms/PiecewiseLinearInterpolation.cpp
@@ -52,13 +52,18 @@ double PiecewiseLinearInterpolation::getValue(double pnt_to_interpolate) const
pnt_to_interpolate));
std::size_t const interval_idx = std::distance(_supp_pnts.begin(), it) - 1;
+ // support points.
+ double const x = _supp_pnts[interval_idx];
+ double const x_r = _supp_pnts[interval_idx + 1];
+
+ // values.
+ double const f = _values_at_supp_pnts[interval_idx];
+ double const f_r = _values_at_supp_pnts[interval_idx + 1];
+
// compute linear interpolation polynom: y = m * (x - support[i]) + value[i]
- const double m((_values_at_supp_pnts[interval_idx + 1] -
- _values_at_supp_pnts[interval_idx]) /
- (_supp_pnts[interval_idx + 1] - _supp_pnts[interval_idx]));
+ const double m = (f_r - f) / (x_r - x);
- return m * (pnt_to_interpolate - _supp_pnts[interval_idx]) +
- _values_at_supp_pnts[interval_idx];
+ return m * (pnt_to_interpolate - x) + f;
}
double PiecewiseLinearInterpolation::getDerivative(
@@ -81,17 +86,21 @@ double PiecewiseLinearInterpolation::getDerivative(
if (interval_idx > 2 && interval_idx < _supp_pnts.size() - 1)
{
- double const tangent_right =
- (_values_at_supp_pnts[interval_idx - 1] -
- _values_at_supp_pnts[interval_idx + 1]) /
- (_supp_pnts[interval_idx - 1] - _supp_pnts[interval_idx + 1]);
- double const tangent_left =
- (_values_at_supp_pnts[interval_idx - 2] -
- _values_at_supp_pnts[interval_idx]) /
- (_supp_pnts[interval_idx - 2] - _supp_pnts[interval_idx]);
- double const w =
- (pnt_to_interpolate - _supp_pnts[interval_idx]) /
- (_supp_pnts[interval_idx - 1] - _supp_pnts[interval_idx]);
+ // left and right support points.
+ double const x_ll = _supp_pnts[interval_idx - 2];
+ double const x_l = _supp_pnts[interval_idx - 1];
+ double const x = _supp_pnts[interval_idx];
+ double const x_r = _supp_pnts[interval_idx + 1];
+
+ // left and right values.
+ double const f_ll = _values_at_supp_pnts[interval_idx - 2];
+ double const f_l = _values_at_supp_pnts[interval_idx - 1];
+ double const f = _values_at_supp_pnts[interval_idx];
+ double const f_r = _values_at_supp_pnts[interval_idx + 1];
+
+ double const tangent_right = (f_l - f_r) / (x_l - x_r);
+ double const tangent_left = (f_ll - f) / (x_ll - x);
+ double const w = (pnt_to_interpolate - x) / (x_l - x);
return (1. - w) * tangent_right + w * tangent_left;
}
else
--
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