From 4cf23e770b966a286daf9b9c3d63f26dfa471634 Mon Sep 17 00:00:00 2001
From: Wenqing Wang <wenqing.wang@ufz.de>
Date: Fri, 4 Nov 2016 16:04:52 +0100
Subject: [PATCH] [Alg] Added a function to get inverse value from curve
---
.../PiecewiseLinearInterpolation.h | 28 ++++++++++++++++++-
.../TestPiecewiseLinearInterpolation.cpp | 27 ++++++++++++++++++
2 files changed, 54 insertions(+), 1 deletion(-)
diff --git a/MathLib/InterpolationAlgorithms/PiecewiseLinearInterpolation.h b/MathLib/InterpolationAlgorithms/PiecewiseLinearInterpolation.h
index 643c87061c1..03f134c69c7 100644
--- a/MathLib/InterpolationAlgorithms/PiecewiseLinearInterpolation.h
+++ b/MathLib/InterpolationAlgorithms/PiecewiseLinearInterpolation.h
@@ -58,7 +58,26 @@ public:
* this interval are set to \f$x_{\min}\f$ or \f$x_{\max}\f$.
* @return The interpolated value.
*/
- double getValue(double pnt_to_interpolate) const;
+ double getValue(double const pnt_to_interpolate) const;
+
+ /**
+ * \brief Calculates the interpolation of the variable by a known
+ * value of the piece wise linear curve. The curve must be
+ * monotonically increase or decrease. The monotonicity can be
+ * checked after create an instance of this class.
+ *
+ * @param value The variable for a point should be located within the range
+ * \f$[f(x_{\min}), f(x_{\max})]\f$, where \f$x_{\min} = \min_{1 \le j \le n}
+ * x_j\f$ and
+ * \f$x_{\max} = \max_{1 \le j \le n} x_j\f$. Points outside of this
+ * interval are
+ * set to f(x_{\min}) or f(x_{\max}).
+ * @return The interpolated value, \f$x\f$.
+ *
+ * \attention Check the monotonicity of the data beforehand if this function
+ * is used.
+ */
+ double getInverseValue(double const value) const;
/**
* \brief Calculates derivative using quadratic interpolation
@@ -76,9 +95,16 @@ public:
double getSupportMax() const;
double getSupportMin() const;
+ bool isMonotonic() const;
+
private:
std::vector<double> _supp_pnts;
std::vector<double> _values_at_supp_pnts;
+
+ double interpolate(std::vector<double> const& supp_pnts,
+ std::vector<double> const& values_at_supp_pnts,
+ std::size_t const interval_idx,
+ double const pnt_to_interpolate) const;
};
} // end namespace MathLib
diff --git a/Tests/MathLib/TestPiecewiseLinearInterpolation.cpp b/Tests/MathLib/TestPiecewiseLinearInterpolation.cpp
index 7a0517a368b..6d241be594d 100644
--- a/Tests/MathLib/TestPiecewiseLinearInterpolation.cpp
+++ b/Tests/MathLib/TestPiecewiseLinearInterpolation.cpp
@@ -156,3 +156,30 @@ TEST(MathLibInterpolationAlgorithms, PiecewiseLinearInterpolationDerivative)
ASSERT_NEAR(0, interpolation.getDerivative(1001),
std::numeric_limits<double>::epsilon());
}
+
+TEST(MathLibInterpolationAlgorithms, PiecewiseLinearInterpolationGetInverseValue)
+{
+ const std::size_t size = 1000;
+ std::vector<double> variables, values;
+ for (std::size_t k=0; k < size; ++k)
+ {
+ variables.push_back(static_cast<double>(k));
+ values.push_back(static_cast<double>(2*k));
+ }
+
+ std::vector<double> variables_cpy = variables;
+ std::vector<double> values_cpy = values;
+
+ MathLib::PiecewiseLinearInterpolation
+ interpolation{std::move(variables_cpy),
+ std::move(values_cpy)};
+
+ ASSERT_EQ(true, interpolation.isMonotonic());
+
+ // Get inverse values and compare them
+ for (std::size_t k=0; k < size; ++k)
+ {
+ ASSERT_NEAR(variables[k], interpolation.getInverseValue(values[k]),
+ std::numeric_limits<double>::epsilon());
+ }
+}
--
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