Added fitting with lmfit (#128)

- added stand alone fitting using:
https://jugit.fz-juelich.de/mlz/lmfit.git
- fit_gaus, fit_pol1 with and without errors
- multi threaded fitting

---------

Co-authored-by: JulianHeymes <julian.heymes@psi.ch>

include/aare/Fit.hpp

@@ -0,0 +1,76 @@
+#pragma once
+
+#include <cmath>
+#include <fmt/core.h>
+#include <vector>
+
+#include "aare/NDArray.hpp"
+
+namespace aare {
+
+namespace func {
+double gaus(const double x, const double *par);
+NDArray<double, 1> gaus(NDView<double, 1> x, NDView<double, 1> par);
+
+double pol1(const double x, const double *par);
+NDArray<double, 1> pol1(NDView<double, 1> x, NDView<double, 1> par);
+
+} // namespace func
+
+static constexpr int DEFAULT_NUM_THREADS = 4;
+
+/**
+ * @brief Fit a 1D Gaussian to data.
+ * @param data data to fit
+ * @param x x values
+ */
+NDArray<double, 1> fit_gaus(NDView<double, 1> x, NDView<double, 1> y);
+
+
+/**
+ * @brief Fit a 1D Gaussian to each pixel. Data layout [row, col, values]
+ * @param x x values
+ * @param y y vales, layout [row, col, values]
+ * @param n_threads number of threads to use
+ */
+NDArray<double, 3> fit_gaus(NDView<double, 1> x, NDView<double, 3> y, int n_threads = DEFAULT_NUM_THREADS);
+
+
+/**
+ * @brief Fit a 1D Gaussian with error estimates
+ * @param x x values
+ * @param y y vales, layout [row, col, values]
+ * @param y_err error in y, layout [row, col, values]
+ * @param par_out output parameters
+ * @param par_err_out output error parameters
+ */
+void fit_gaus(NDView<double, 1> x, NDView<double, 1> y, NDView<double, 1> y_err,
+              NDView<double, 1> par_out, NDView<double, 1> par_err_out);
+
+/**
+ * @brief Fit a 1D Gaussian to each pixel with error estimates. Data layout [row, col, values]
+ * @param x x values
+ * @param y y vales, layout [row, col, values]
+ * @param y_err error in y, layout [row, col, values]
+ * @param par_out output parameters, layout [row, col, values]
+ * @param par_err_out output parameter errors, layout [row, col, values]
+ * @param n_threads number of threads to use
+ */
+void fit_gaus(NDView<double, 1> x, NDView<double, 3> y, NDView<double, 3> y_err,
+              NDView<double, 3> par_out, NDView<double, 3> par_err_out, int n_threads = DEFAULT_NUM_THREADS);
+
+
+NDArray<double, 1> fit_pol1(NDView<double, 1> x, NDView<double, 1> y);
+
+NDArray<double, 3> fit_pol1(NDView<double, 1> x, NDView<double, 3> y, int n_threads = DEFAULT_NUM_THREADS);
+
+void fit_pol1(NDView<double, 1> x, NDView<double, 1> y,
+                NDView<double, 1> y_err, NDView<double, 1> par_out,
+                NDView<double, 1> par_err_out);
+
+//TODO! not sure we need to offer the different version in C++
+void fit_pol1(NDView<double, 1> x, NDView<double, 3> y,
+                NDView<double, 3> y_err, NDView<double, 3> par_out,
+                NDView<double, 3> par_err_out, int n_threads = DEFAULT_NUM_THREADS);
+
+} // namespace aare

include/aare/utils/task.hpp

@@ -0,0 +1,8 @@
+
+#include <utility>
+#include <vector>
+
+namespace aare {
+std::vector<std::pair<int, int>> split_task(int first, int last, int n_threads);
+
+} // namespace aare