feat: Created midpoint integration numerical method (#1785)

* Created composite Simpson's numerical integration method

* Created midpoint numerical integration method

* Corrections

* Midpoint method

* Improved Documentation

* added namespace numerical_methods

* Update numerical_methods/midpoint_integral_method.cpp

Co-authored-by: David Leal <halfpacho@gmail.com>

* Update numerical_methods/midpoint_integral_method.cpp

Co-authored-by: David Leal <halfpacho@gmail.com>

* Update numerical_methods/midpoint_integral_method.cpp

Co-authored-by: David Leal <halfpacho@gmail.com>

* updating DIRECTORY.md

* clang-format and clang-tidy fixes for ec5e0cce

* Update numerical_methods/midpoint_integral_method.cpp

Co-authored-by: David Leal <halfpacho@gmail.com>

* clang-format and clang-tidy fixes for 7f16cc14

* Update numerical_methods/midpoint_integral_method.cpp

Co-authored-by: David Leal <halfpacho@gmail.com>

* Update midpoint_integral_method.cpp

* All changes have been applied

* clang-format and clang-tidy fixes for 6617e060

* Update numerical_methods/midpoint_integral_method.cpp

Co-authored-by: David Leal <halfpacho@gmail.com>

* Update numerical_methods/midpoint_integral_method.cpp

Co-authored-by: David Leal <halfpacho@gmail.com>

* clang-format and clang-tidy fixes for a5a50f89

* Update numerical_methods/midpoint_integral_method.cpp

Co-authored-by: David Leal <halfpacho@gmail.com>

* clang-format and clang-tidy fixes for 4c60e180

* Create midpoint_integral_method.cpp

* Update numerical_methods/midpoint_integral_method.cpp

Co-authored-by: David Leal <halfpacho@gmail.com>

* clang-format and clang-tidy fixes for 27f76052

* Update midpoint_integral_method.cpp

Co-authored-by: ggkogkou <ggkogkou@ggkogkou.gr>
Co-authored-by: David Leal <halfpacho@gmail.com>
Co-authored-by: github-actions <${GITHUB_ACTOR}@users.noreply.github.com>

DIRECTORY.md

@@ -229,6 +229,7 @@
   * [Golden Search Extrema](https://github.com/TheAlgorithms/C-Plus-Plus/blob/master/numerical_methods/golden_search_extrema.cpp)
   * [Lu Decompose](https://github.com/TheAlgorithms/C-Plus-Plus/blob/master/numerical_methods/lu_decompose.cpp)
   * [Lu Decomposition](https://github.com/TheAlgorithms/C-Plus-Plus/blob/master/numerical_methods/lu_decomposition.h)
+  * [Midpoint Integral Method](https://github.com/TheAlgorithms/C-Plus-Plus/blob/master/numerical_methods/midpoint_integral_method.cpp)
   * [Newton Raphson Method](https://github.com/TheAlgorithms/C-Plus-Plus/blob/master/numerical_methods/newton_raphson_method.cpp)
   * [Ode Forward Euler](https://github.com/TheAlgorithms/C-Plus-Plus/blob/master/numerical_methods/ode_forward_euler.cpp)
   * [Ode Midpoint Euler](https://github.com/TheAlgorithms/C-Plus-Plus/blob/master/numerical_methods/ode_midpoint_euler.cpp)

graph/is_graph_bipartite2.cpp

@@ -10,13 +10,14 @@
  * In this implementation, using a graph in the form of adjacency
  * list, check whether the given graph is a bipartite or not.
  *
- * References used: [GeeksForGeeks](https://www.geeksforgeeks.org/bipartite-graph/)
+ * References used:
+ * [GeeksForGeeks](https://www.geeksforgeeks.org/bipartite-graph/)
  * @author [tushar2407](https://github.com/tushar2407)
  */
+#include <cassert>   /// for assert
 #include <iostream>  /// for IO operations
 #include <queue>     /// for queue data structure
 #include <vector>    /// for vector data structure
-#include <cassert>  /// for assert
 
 /**
  * @namespace graph
@@ -32,32 +33,31 @@ namespace graph {
  * traversed or not yet
  * @returns boolean
  */
-bool checkBipartite(
+bool checkBipartite(const std::vector<std::vector<int64_t>> &graph,
-    const std::vector<std::vector<int64_t>> &graph, 
+                    int64_t index, std::vector<int64_t> *visited) {
-    int64_t index, 
-    std::vector<int64_t> *visited
-)
-{
     std::queue<int64_t> q;  ///< stores the neighbouring node indexes in squence
                             /// of being reached
     q.push(index);          /// insert the current node into the queue
     (*visited)[index] = 1;  /// mark the current node as travelled
-    while(q.size())
+    while (q.size()) {
-    {
         int64_t u = q.front();
         q.pop();
-        for(uint64_t i=0;i<graph[u].size();i++)
+        for (uint64_t i = 0; i < graph[u].size(); i++) {
-        {
+            int64_t v =
-            int64_t v = graph[u][i];    ///< stores the neighbour of the current node
+                graph[u][i];     ///< stores the neighbour of the current node
-            if(!(*visited)[v])          /// check whether the neighbour node is 
+            if (!(*visited)[v])  /// check whether the neighbour node is
                                  /// travelled already or not
             {
-                (*visited)[v] = ((*visited)[u]==1)?-1:1;  /// colour the neighbouring node with 
+                (*visited)[v] =
+                    ((*visited)[u] == 1)
+                        ? -1
+                        : 1;  /// colour the neighbouring node with
                               /// different colour than the current node
                 q.push(v);    /// insert the neighbouring node into the queue
-            }
+            } else if ((*visited)[v] ==
-            else if((*visited)[v] == (*visited)[u])   /// if both the current node and its neighbour
+                       (*visited)[u])  /// if both the current node and its
-                                                      /// has the same state then it is not a bipartite graph
+                                       /// neighbour has the same state then it
+                                       /// is not a bipartite graph
             {
                 return false;
             }
@@ -72,18 +72,18 @@ bool checkBipartite(
  * and values in that row signify the nodes it is connected to
  * @returns booleans
  */
-bool isBipartite(const std::vector<std::vector<int64_t>> &graph) 
+bool isBipartite(const std::vector<std::vector<int64_t>> &graph) {
-{
+    std::vector<int64_t> visited(
-    std::vector<int64_t> visited(graph.size()); ///< stores boolean values 
+        graph.size());  ///< stores boolean values
-                                                /// which signify whether that node had been visited or not
+                        /// which signify whether that node had been visited or
+                        /// not
 
-    for(uint64_t i=0;i<graph.size();i++)
+    for (uint64_t i = 0; i < graph.size(); i++) {
-    {    
+        if (!visited[i])  /// if the current node is not visited then check
-        if(!visited[i]) /// if the current node is not visited then check 
+                          /// whether the sub-graph of that node is a bipartite
-                        /// whether the sub-graph of that node is a bipartite or not
+                          /// or not
-        {
-            if(!checkBipartite(graph, i, &visited))
         {
+            if (!checkBipartite(graph, i, &visited)) {
                 return false;
             }
         }
@@ -96,26 +96,18 @@ bool isBipartite(const std::vector<std::vector<int64_t>> &graph)
  * @brief Self-test implementations
  * @returns void
  */
-static void test()
+static void test() {
-{
+    std::vector<std::vector<int64_t>> graph = {{1, 3}, {0, 2}, {1, 3}, {0, 2}};
-    std::vector<std::vector<int64_t>> graph = {
-        {1,3},
-        {0,2},
-        {1,3},
-        {0,2}
-    };
 
-    assert(graph::isBipartite(graph) == true); /// check whether the above 
+    assert(graph::isBipartite(graph) ==
+           true);  /// check whether the above
                    /// defined graph is indeed bipartite
 
     std::vector<std::vector<int64_t>> graph_not_bipartite = {
-        {1,2,3},
+        {1, 2, 3}, {0, 2}, {0, 1, 3}, {0, 2}};
-        {0,2},
-        {0,1,3},
-        {0,2}
-    };
 
-    assert(graph::isBipartite(graph_not_bipartite) == false); /// check whether 
+    assert(graph::isBipartite(graph_not_bipartite) ==
+           false);  /// check whether
                     /// the above defined graph is indeed bipartite
     std::cout << "All tests have successfully passed!\n";
 }
@@ -127,8 +119,7 @@ static void test()
  * graph is bipartite or not.
  * @returns 0 on exit
  */
-int main()
+int main() {
-{
     test();  // run self-test implementations
     return 0;
 }

numerical_methods/midpoint_integral_method.cpp

@@ -0,0 +1,199 @@
+/**
+ * @file
+ * @brief A numerical method for easy [approximation of
+ * integrals](https://en.wikipedia.org/wiki/Midpoint_method)
+ * @details The idea is to split the interval into N of intervals and use as
+ * interpolation points the xi for which it applies that xi = x0 + i*h, where h
+ * is a step defined as h = (b-a)/N where a and b are the first and last points
+ * of the interval of the integration [a, b].
+ *
+ * We create a table of the xi and their corresponding f(xi) values and we
+ * evaluate the integral by the formula: I = h * {f(x0+h/2) + f(x1+h/2) + ... +
+ * f(xN-1+h/2)}
+ *
+ * Arguments can be passed as parameters from the command line argv[1] = N,
+ * argv[2] = a, argv[3] = b. In this case if the default values N=16, a=1, b=3
+ * are changed then the tests/assert are disabled.
+ *
+ *
+ * @author [ggkogkou](https://github.com/ggkogkou)
+ */
+#include <cassert>     /// for assert
+#include <cmath>       /// for math functions
+#include <cstdint>     /// for integer allocation
+#include <cstdlib>     /// for std::atof
+#include <functional>  /// for std::function
+#include <iostream>    /// for IO operations
+#include <map>         /// for std::map container
+
+/**
+ * @namespace numerical_methods
+ * @brief Numerical algorithms/methods
+ */
+namespace numerical_methods {
+/**
+ * @namespace midpoint_rule
+ * @brief Functions for the [Midpoint
+ * Integral](https://en.wikipedia.org/wiki/Midpoint_method) method
+ * implementation
+ */
+namespace midpoint_rule {
+/**
+ * @fn double midpoint(const std::int32_t N, const double h, const double a,
+ * const std::function<double (double)>& func)
+ * @brief Main function for implementing the Midpoint Integral Method
+ * implementation
+ * @param N is the number of intervals
+ * @param h is the step
+ * @param a is x0
+ * @param func is the function that will be integrated
+ * @returns the result of the integration
+ */
+double midpoint(const std::int32_t N, const double h, const double a,
+                const std::function<double(double)>& func) {
+    std::map<int, double>
+        data_table;  // Contains the data points, key: i, value: f(xi)
+    double xi = a;   // Initialize xi to the starting point x0 = a
+
+    // Create the data table
+    // Loop from x0 to xN-1
+    double temp = NAN;
+    for (std::int32_t i = 0; i < N; i++) {
+        temp = func(xi + h / 2);  // find f(xi+h/2)
+        data_table.insert(
+            std::pair<std::int32_t, double>(i, temp));  // add i and f(xi)
+        xi += h;  // Get the next point xi for the next iteration
+    }
+
+    // Evaluate the integral.
+    // Remember: {f(x0+h/2) + f(x1+h/2) + ... + f(xN-1+h/2)}
+    double evaluate_integral = 0;
+    for (std::int32_t i = 0; i < N; i++) evaluate_integral += data_table.at(i);
+
+    // Multiply by the coefficient h
+    evaluate_integral *= h;
+
+    // If the result calculated is nan, then the user has given wrong input
+    // interval.
+    assert(!std::isnan(evaluate_integral) &&
+           "The definite integral can't be evaluated. Check the validity of "
+           "your input.\n");
+    // Else return
+    return evaluate_integral;
+}
+
+/**
+ * @brief A function f(x) that will be used to test the method
+ * @param x The independent variable xi
+ * @returns the value of the dependent variable yi = f(xi) = sqrt(xi) + ln(xi)
+ */
+double f(double x) { return std::sqrt(x) + std::log(x); }
+/**
+ * @brief A function g(x) that will be used to test the method
+ * @param x The independent variable xi
+ * @returns the value of the dependent variable yi = g(xi) = e^(-xi) * (4 -
+ * xi^2)
+ */
+double g(double x) { return std::exp(-x) * (4 - std::pow(x, 2)); }
+/**
+ * @brief A function k(x) that will be used to test the method
+ * @param x The independent variable xi
+ * @returns the value of the dependent variable yi = k(xi) = sqrt(2*xi^3 + 3)
+ */
+double k(double x) { return std::sqrt(2 * std::pow(x, 3) + 3); }
+/**
+ * @brief A function l(x) that will be used to test the method
+ * @param x The independent variable xi
+ * @returns the value of the dependent variable yi = l(xi) = xi + ln(2*xi + 1)
+ */
+double l(double x) { return x + std::log(2 * x + 1); }
+
+}  // namespace midpoint_rule
+}  // namespace numerical_methods
+
+/**
+ * @brief Self-test implementations
+ * @param N is the number of intervals
+ * @param h is the step
+ * @param a is x0
+ * @param b is the end of the interval
+ * @param used_argv_parameters is 'true' if argv parameters are given and
+ * 'false' if not
+ */
+static void test(std::int32_t N, double h, double a, double b,
+                 bool used_argv_parameters) {
+    // Call midpoint() for each of the test functions f, g, k, l
+    // Assert with two decimal point precision
+    double result_f = numerical_methods::midpoint_rule::midpoint(
+        N, h, a, numerical_methods::midpoint_rule::f);
+    assert((used_argv_parameters || (result_f >= 4.09 && result_f <= 4.10)) &&
+           "The result of f(x) is wrong");
+    std::cout << "The result of integral f(x) on interval [" << a << ", " << b
+              << "] is equal to: " << result_f << std::endl;
+
+    double result_g = numerical_methods::midpoint_rule::midpoint(
+        N, h, a, numerical_methods::midpoint_rule::g);
+    assert((used_argv_parameters || (result_g >= 0.27 && result_g <= 0.28)) &&
+           "The result of g(x) is wrong");
+    std::cout << "The result of integral g(x) on interval [" << a << ", " << b
+              << "] is equal to: " << result_g << std::endl;
+
+    double result_k = numerical_methods::midpoint_rule::midpoint(
+        N, h, a, numerical_methods::midpoint_rule::k);
+    assert((used_argv_parameters || (result_k >= 9.06 && result_k <= 9.07)) &&
+           "The result of k(x) is wrong");
+    std::cout << "The result of integral k(x) on interval [" << a << ", " << b
+              << "] is equal to: " << result_k << std::endl;
+
+    double result_l = numerical_methods::midpoint_rule::midpoint(
+        N, h, a, numerical_methods::midpoint_rule::l);
+    assert((used_argv_parameters || (result_l >= 7.16 && result_l <= 7.17)) &&
+           "The result of l(x) is wrong");
+    std::cout << "The result of integral l(x) on interval [" << a << ", " << b
+              << "] is equal to: " << result_l << std::endl;
+}
+
+/**
+ * @brief Main function
+ * @param argc commandline argument count (ignored)
+ * @param argv commandline array of arguments (ignored)
+ * @returns 0 on exit
+ */
+int main(int argc, char** argv) {
+    std::int32_t N =
+        16;  /// Number of intervals to divide the integration interval.
+    /// MUST BE EVEN
+    double a = 1, b = 3;  /// Starting and ending point of the integration in
+    /// the real axis
+    double h = NAN;  /// Step, calculated by a, b and N
+
+    bool used_argv_parameters =
+        false;  // If argv parameters are used then the assert must be omitted
+    // for the test cases
+
+    // Get user input (by the command line parameters or the console after
+    // displaying messages)
+    if (argc == 4) {
+        N = std::atoi(argv[1]);
+        a = std::atof(argv[2]);
+        b = std::atof(argv[3]);
+        // Check if a<b else abort
+        assert(a < b && "a has to be less than b");
+        assert(N > 0 && "N has to be > 0");
+        if (N < 4 || a != 1 || b != 3) {
+            used_argv_parameters = true;
+        }
+        std::cout << "You selected N=" << N << ", a=" << a << ", b=" << b
+                  << std::endl;
+    } else {
+        std::cout << "Default N=" << N << ", a=" << a << ", b=" << b
+                  << std::endl;
+    }
+
+    // Find the step
+    h = (b - a) / N;
+
+    test(N, h, a, b, used_argv_parameters);  // run self-test implementations
+
+    return 0;
+}