3 files changed, 38 insertions, 14 deletions

diff --git a/libprakpp/include/prakmath.hpp b/libprakpp/include/prakmath.hpp
index ebd02bf..bb09e74 100644
--- a/libprakpp/include/prakmath.hpp
+++ b/libprakpp/include/prakmath.hpp
@@ -289,6 +289,22 @@ pvalue<T> function(function_t<T> func, const std::vector<pvalue<T>> &args) {
 	return ret;
 }
 
+template <typename iterator, typename T = iterator::value_type>
+requires requires(iterator a){ ++a; *a; } && (std::integral<T> || std::floating_point<T>)
+T discrete_integral_trapezoid(iterator X_start, iterator X_end, iterator Y_start, iterator Y_end)
+{
+	T ret = 0;
+	for (T Xl = *X_start, Yl = *Y_start; 
+	     X_start != X_end && Y_start != Y_end; 
+	     ++X_start, ++Y_start) 
+	{
+		ret += std::abs(*X_start - Xl) * (*Y_start + Yl) / 2; // first iteration will add 0
+		Xl = *X_start;
+		Yl = *Y_start;
+	}
+	return ret;
+}
+
 /// calculate least-squares linear approximation to fit data
 /// ax+b = y (ss is an error of Y value)
 template <std::floating_point T>
diff --git a/libprakpp/include/prakmatrix.hpp b/libprakpp/include/prakmatrix.hpp
index 53d3b4b..f1ccddc 100644
--- a/libprakpp/include/prakmatrix.hpp
+++ b/libprakpp/include/prakmatrix.hpp
@@ -14,7 +14,7 @@ struct dimension_error : public std::logic_error {
 };
 
 /// A class to represent a matrix. Works as an extension to std::vector, so all methods of std::vector are available on this class
-/// BIG TODO: replave `throw` with `std::optional` return type
+/// BIG TODO: replace `throw` with `std::optional` return type
 template <typename T>
 struct matrix : public std::vector<T> {
 	size_t rows, cols;
@@ -75,7 +75,7 @@ struct matrix : public std::vector<T> {
 	}
 	/// multiply matrix by a scalar
 	template <typename Arg>
-	std::enable_if_t<std::is_arithmetic_v<Arg>, struct matrix<T>> 
+	std::enable_if_t<std::is_arithmetic_v<Arg>, struct matrix<T>>::type
 	operator*(const Arg other) const {
 		struct matrix<T> ret(rows, cols);
 		for (size_t i = 0; i < this->size(); ++i)
diff --git a/libprakpp/include/praktable.hpp b/libprakpp/include/praktable.hpp
index f00e7b9..1870ec6 100644
--- a/libprakpp/include/praktable.hpp
+++ b/libprakpp/include/praktable.hpp
@@ -222,6 +222,14 @@ public:
 		return data.at(names.size() * row + column);
 	}
 
+	const dtype & SUBSCR_OPRTR (const std::string &column, size_t row) const noexcept(false) {
+		size_t i = index(column);
+		return data.at(names.size() * row + index(column));
+	}
+
+	const dtype & SUBSCR_OPRTR (size_t column, size_t row) const {
+		return data.at(names.size() * row + column);
+	}
 	// prints a table. defaults to using std::cout, but any std::ostream can be passed in it.
 	void print(std::ostream &stream = std::cout) const {
 		stream << "columns: " << columns << ", rows: " << rows << std::endl;
@@ -493,7 +501,7 @@ public:
 
 	// returns an std::pair with coefficients A and B in that order
 	std::pair<prak::pvalue<dtype>, prak::pvalue<dtype>> 
-	least_squares_linear(std::string x, std::string y, std::optional<std::string> sigma, std::optional<dtype> sigma_fixed) 
+	least_squares_linear(std::string x, std::string y, std::optional<std::string> sigma, std::optional<dtype> sigma_fixed) const
 	noexcept(false) {
 		if (sigma.has_value() == sigma_fixed.has_value()) 
 			throw std::invalid_argument("sigma and sigma_fixed can't both have (no) value");
@@ -501,9 +509,9 @@ public:
 		prak::vector<dtype> _y(rows);
 		prak::vector<dtype> _s(rows);
 
-		std::copy(begin(x), end(x), _x.begin());
-		std::copy(begin(y), end(y), _y.begin());
-		if (sigma.has_value()) std::copy(begin(*sigma), end(*sigma), _s.begin());
+		std::copy(cbegin(x), cend(x), _x.begin());
+		std::copy(cbegin(y), cend(y), _y.begin());
+		if (sigma.has_value()) std::copy(cbegin(*sigma), cend(*sigma), _s.begin());
 		else _s = prak::vector<dtype>(rows, static_cast<dtype>(*sigma_fixed));
 
 		std::pair<prak::pvalue<dtype>, prak::pvalue<dtype>> ret;
@@ -512,31 +520,31 @@ public:
 	}
 
 	// calculate an average of the column 
-	dtype col_avg(const std::string &column) {
+	dtype col_avg(const std::string &column) const {
 		dtype accum = dtype{};
-		for (auto it = begin(column); it != end(column); ++it) 
+		for (auto it = cbegin(column); it != cend(column); ++it) 
 			accum += *it;
 		return accum / rows;
 	}
 
-	dtype col_max(const std::string &column) {
+	dtype col_max(const std::string &column) const {
 		dtype max = dtype{};
-		for (auto it = begin(column); it != end(column); ++it) 
+		for (auto it = cbegin(column); it != cend(column); ++it) 
 			max = max < *it ? *it : max;
 		return max;
 	}
-	dtype col_min(const std::string &column) {
+	dtype col_min(const std::string &column) const {
 		dtype min = dtype{};
-		for (auto it = begin(column); it != end(column); ++it) 
+		for (auto it = cbegin(column); it != cend(column); ++it) 
 			min = min > *it ? *it : min;
 		return min;
 	}
 
 	// calculate standard deviation of the column
-	dtype col_stddev(const std::string &column) {
+	dtype col_stddev(const std::string &column) const {
 		dtype accum = dtype{};
 		dtype avg = col_avg(column);
-		for (auto it = begin(column); it != end(column); ++it)
+		for (auto it = cbegin(column); it != cend(column); ++it)
 			accum += (*it - avg)*(*it - avg);
 		return std::sqrt(accum / rows);
 	}