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97 lines
2.6 KiB
C++
97 lines
2.6 KiB
C++
#ifndef OPENMC_INTERPOLATE_H
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#define OPENMC_INTERPOLATE_H
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#include <cmath>
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#include <vector>
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#include "openmc/error.h"
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#include "openmc/search.h"
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#include "openmc/span.h"
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namespace openmc {
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inline double interpolate_lin_lin(
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double x0, double x1, double y0, double y1, double x)
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{
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return y0 + (x - x0) / (x1 - x0) * (y1 - y0);
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}
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inline double interpolate_lin_log(
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double x0, double x1, double y0, double y1, double x)
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{
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return y0 + std::log(x / x0) / std::log(x1 / x0) * (y1 - y0);
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}
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inline double interpolate_log_lin(
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double x0, double x1, double y0, double y1, double x)
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{
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return y0 * std::exp((x - x0) / (x1 - x0) * std::log(y1 / y0));
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}
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inline double interpolate_log_log(
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double x0, double x1, double y0, double y1, double x)
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{
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double f = std::log(x / x0) / std::log(x1 / x0);
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return y0 * std::exp(f * std::log(y1 / y0));
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}
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inline double interpolate_lagrangian(
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span<const double> xs, span<const double> ys, int idx, double x, int order)
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{
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double output {0.0};
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for (int i = 0; i < order + 1; i++) {
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double numerator {1.0};
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double denominator {1.0};
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for (int j = 0; j < order + 1; j++) {
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if (i == j)
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continue;
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numerator *= (x - xs[idx + j]);
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denominator *= (xs[idx + i] - xs[idx + j]);
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}
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output += (numerator / denominator) * ys[idx + i];
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}
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return output;
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}
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inline double interpolate(span<const double> xs, span<const double> ys,
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double x, Interpolation i = Interpolation::lin_lin)
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{
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int idx = lower_bound_index(xs.begin(), xs.end(), x);
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if (idx == xs.size())
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idx--;
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switch (i) {
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case Interpolation::histogram:
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return ys[idx];
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case Interpolation::lin_lin:
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return interpolate_lin_lin(xs[idx], xs[idx + 1], ys[idx], ys[idx + 1], x);
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case Interpolation::log_log:
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return interpolate_log_log(xs[idx], xs[idx + 1], ys[idx], ys[idx + 1], x);
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case Interpolation::lin_log:
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return interpolate_lin_log(xs[idx], xs[idx + 1], ys[idx], ys[idx + 1], x);
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case Interpolation::log_lin:
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return interpolate_log_lin(xs[idx], xs[idx + 1], ys[idx], ys[idx + 1], x);
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case Interpolation::quadratic:
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// move back one point if x is in the last interval of the x-grid
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if (idx == xs.size() - 2 && idx > 0)
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idx--;
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return interpolate_lagrangian(xs, ys, idx, x, 2);
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case Interpolation::cubic:
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// if x is not in the first interval of the x-grid, move back one
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if (idx > 0)
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idx--;
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// if the index was the last interval of the x-grid, move it back one more
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if (idx == xs.size() - 3)
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idx--;
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return interpolate_lagrangian(xs, ys, idx, x, 3);
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default:
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fatal_error("Unsupported interpolation");
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}
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}
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} // namespace openmc
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#endif
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