From b0fd7226739440062e40e61f7f03ceed533d53c1 Mon Sep 17 00:00:00 2001
From: weiguang cui <cuiweiguang@gmail.com>
Date: Sat, 6 Apr 2024 12:32:31 +0200
Subject: [PATCH] adding pi

---
 CodingTutorialC++/CMakeLists.txt |  3 +-
 CodingTutorialC++/Makefile       |  8 +++--
 CodingTutorialC++/README.md      | 12 +++++++
 CodingTutorialC++/pi.cpp         | 62 ++++++++++++++++++++++++++++++++
 4 files changed, 81 insertions(+), 4 deletions(-)
 create mode 100644 CodingTutorialC++/pi.cpp

diff --git a/CodingTutorialC++/CMakeLists.txt b/CodingTutorialC++/CMakeLists.txt
index 2453ff2..e08ec15 100644
--- a/CodingTutorialC++/CMakeLists.txt
+++ b/CodingTutorialC++/CMakeLists.txt
@@ -5,4 +5,5 @@ set(CMAKE_CXX_STANDARD 11)
 
 add_executable(ACO_practice overflow.cpp
         MainArgs.cpp
-        openmp-example.cpp)
+        openmp-example.cpp
+        pi.cpp)
diff --git a/CodingTutorialC++/Makefile b/CodingTutorialC++/Makefile
index 1e5b53e..54c1f63 100644
--- a/CodingTutorialC++/Makefile
+++ b/CodingTutorialC++/Makefile
@@ -8,19 +8,18 @@ CXXFLAGS = -std=c++11 -Wall -fopenmp
 TARGET = ACO_practice
 
 # Source files
-SRCS = overflow.cpp MainArgs.cpp openmp-example.cpp
+SRCS = overflow.cpp MainArgs.cpp openmp-example.cpp pi.cpp
 
 # Object files
 OBJS = $(SRCS:.cpp=.o)
 
 # Executables
-EXECS = overflow MainArgs openmp-example
+EXECS = overflow MainArgs openmp-example pi
 
 OMP_NUM_THREADS=4
 export OMP_NUM_THREADS
 
 all: $(TARGET)
-	./openmp-example
 
 overflow: overflow.o
 	$(CXX) $(CXXFLAGS) -o overflow overflow.o
@@ -31,6 +30,9 @@ MainArgs: MainArgs.o
 openmp-example: openmp-example.o
 	$(CXX) $(CXXFLAGS) -o openmp-example openmp-example.o
 
+pi: pi.o
+	$(CXX) $(CXXFLAGS) -o pi pi.o
+
 .cpp.o:
 	$(CXX) $(CXXFLAGS) -c $<  -o $@
 
diff --git a/CodingTutorialC++/README.md b/CodingTutorialC++/README.md
index 2433003..26cf343 100644
--- a/CodingTutorialC++/README.md
+++ b/CodingTutorialC++/README.md
@@ -16,6 +16,16 @@ This file contains a program that prints the name of the program and all the arg
 
 This file contains a program that uses OpenMP to calculate the sum of numbers from 1 to 1e5. It sets the number of threads to the number of processors available, and each thread calculates a portion of the sum.
 
+### [`pi.cpp`](./pi.cpp)
+
+This file contains a program that calculates the value of pi using the Leibniz formula for π. The program uses OpenMP for parallel computation, allowing it to calculate pi to a high degree of precision in a shorter amount of time. The number of threads used for the computation can be specified as a command-line argument when running the program.
+To build and run `pi.cpp`, use the make command followed by the name of the file (without the .cpp extension), and then run the resulting executable with the number of threads as an argument:
+
+```bash
+make pi
+./pi 4 This will build `pi.cpp` and run the resulting `pi` executable with 4 threads.
+```
+
 ## Build Files
 
 ### [`Makefile`](./Makefile)
@@ -38,6 +48,8 @@ To build individual files, use the make command followed by the name of the file
 ```bash
 make overflow
 make MainArgs
+make openmp-example
+make pi
 ```
 
 To clean up the built files, use the make clean command:
diff --git a/CodingTutorialC++/pi.cpp b/CodingTutorialC++/pi.cpp
new file mode 100644
index 0000000..cdbcfe8
--- /dev/null
+++ b/CodingTutorialC++/pi.cpp
@@ -0,0 +1,62 @@
+//
+// Created by weiguang on 6/04/24.
+//
+#include <cmath>
+#include <cstddef>
+#include <cstdlib>
+#include <cstring>
+#include <iostream>
+#include <cstdint>
+#include <omp.h>
+#include <ctime>
+#include <iomanip>
+
+#define INFTY ((uint64_t)1<<30)
+
+int main(int argc, char **argv)
+{
+  uint64_t k;
+  double pi;
+  time_t tstart, tend;
+  int    nthreads_to_be_used;
+
+  if(argc != 2) {
+    std::cerr << "usage: ./pi NTHREADS\nABORTING\n";
+    return 1;
+  }
+
+  nthreads_to_be_used = std::atoi(argv[1]);
+  std::cerr << "using " << nthreads_to_be_used << " threads for execution\n";
+  omp_set_num_threads(nthreads_to_be_used);
+
+#pragma omp parallel shared(std::cerr) default(none)
+  {
+    // all private by construction
+    int nthreads, ncpus, ithread, omp_num_threads;
+
+    // who am I?
+    ithread = omp_get_thread_num();
+
+    /* only one thread (==0) does this */
+    if (ithread == 0)
+    {
+      ncpus       = omp_get_num_procs();
+      nthreads    = omp_get_num_threads();
+      std::cerr << "ncpus=" << ncpus << " nthreads=" << nthreads << "\n";
+    }
+  }
+
+  pi = 0.0;
+
+  tstart = time(NULL);
+#pragma omp parallel for default(none) private(k) reduction(+:pi) schedule(static)
+  for(k=0; k<INFTY; k++) {
+    pi += std::pow(-1.0/3.0, (double)k) / (2.*(double)k+1.);
+  }
+  tend = time(NULL);
+
+  pi *= std::sqrt(12);
+  std::cerr << "pi = " << std::fixed << std::setprecision(12) << pi << " (time=" << std::difftime(tend,tstart) << " [sec])\n";
+
+  return 0;
+}
\ No newline at end of file