commit 9c3c4ad068c0322d5e7aff464ee732fd42af9c2a
Author: niklas <niklas.birk.nb@gmail.com>
Date:   Wed Nov 22 19:51:30 2023 +0100

    Initial

diff --git a/uebung_01/exercise_1.py b/uebung_01/exercise_1.py
new file mode 100644
index 0000000..5ee8612
--- /dev/null
+++ b/uebung_01/exercise_1.py
@@ -0,0 +1,22 @@
+import numpy as np
+
+for n in [3,5,10,100,1000]:
+    A = np.zeros((n,n))
+    x = np.zeros((n,1))
+    y_c = np.zeros((n,1))
+
+    for i in range(0,n):
+        x[i] = i+1
+        y_c[i] = (i+1) * n;
+
+        for j in range(0,n):
+            A[i,j] =(i+1) / (j+1)
+
+    y = A@x
+    
+    if n == 3 or n == 5:
+        print(x)
+        print(A)
+        print(y)
+
+    print("Fuer n =",n,":",np.linalg.norm(y - y_c))
diff --git a/uebung_01/exercise_2a.py b/uebung_01/exercise_2a.py
new file mode 100644
index 0000000..a9d3653
--- /dev/null
+++ b/uebung_01/exercise_2a.py
@@ -0,0 +1,24 @@
+import numpy as np
+import matplotlib.pyplot as plt
+
+# x = np.linspace(0, 2 * np.pi, 100)
+x_1 = np.arange(0, 2 * np.pi, 1)
+x_0_5 = np.arange(0, 2 * np.pi, 0.5)
+x_0_1 = np.arange(0, 2 * np.pi, 0.1)
+
+y_s_1 = np.sin(x_1)
+y_s_0_5 = np.sin(x_0_5)
+y_s_0_1 = np.sin(x_0_1)
+y_c = np.cos(x_1)
+
+plt.plot(x_1,y_s_1,"purple", label="sin(x) with stepsize 1")
+plt.plot(x_0_5,y_s_0_5,"pink", label="sin(x) with stepsize 0.5")
+plt.plot(x_0_1,y_s_0_1,"red", label="sin(x) with stepsize 0.1")
+plt.plot(x_1,y_c,"green", label="cos(x)")
+
+plt.title("A2.a) Sine and Cosine")
+plt.xlabel("x")
+plt.ylabel("y")
+plt.legend()
+
+plt.show()   
diff --git a/uebung_01/exercise_2b.py b/uebung_01/exercise_2b.py
new file mode 100644
index 0000000..ed7c67c
--- /dev/null
+++ b/uebung_01/exercise_2b.py
@@ -0,0 +1,22 @@
+import numpy as np
+import matplotlib.pyplot as plt
+
+plt.rcParams['text.usetex'] = True
+
+# x = np.linspace(0, 2 * np.pi, 100)
+x = np.arange(-2, 2, 0.1)
+
+f = np.exp(-x**2)
+g = np.sin(x**2)
+h = np.sin(1 / (x**3 + 9))
+
+plt.plot(x, f, "purple", label=r"$f(x) = \exp(-x^2)$")
+plt.plot(x, g, "red", label=r"$g(x) = \sin(x^2)$")
+plt.plot(x, h, "green", label=r"$h(x) = \frac{1}{x^3 + 9}$")
+
+plt.title("A2.b)")
+plt.xlabel("x")
+plt.ylabel("y")
+plt.legend()
+
+plt.show()   
diff --git a/uebung_01/exercise_3.py b/uebung_01/exercise_3.py
new file mode 100644
index 0000000..da1d328
--- /dev/null
+++ b/uebung_01/exercise_3.py
@@ -0,0 +1,68 @@
+import numpy as np
+import matplotlib.pyplot as plt
+
+def runge(x):
+    return 1 / (1 + 25 * x**2)
+
+def divided_differences(x, y):
+    n = len(y)
+    a = np.zeros((n,n))
+    
+    a[:,0] = y
+    
+    for i in range(1,n):
+        for j in range(1,i+1):
+            a[i,j] = (a[i,j-1] - a[i-1,j-1]) / (x[i] - x[i-j]) # (links daneben - links darüber) / (x[zeile] - x[zeile - spalte])
+    
+    return a
+    
+def newton_interpolation(a, data, x):
+    n = len(a)
+    
+    p = np.zeros(len(x))
+    
+    for i in range(1,n+1):
+        p = a[n-i] + (x - data[n-i]) * p # Horner Schema; '-' and '*' are overloaded for numpy arrays: so at least one argument 'data' or 'x' has to be numpy array 
+    
+    return p
+
+####################################################################################################################################################################
+n = 12
+
+x = np.linspace(-1, 1, 200)
+x_e = np.linspace(-1, 1, n) # equidistant grid points
+
+# Chebyshev grid points
+x_c = np.zeros(n)
+for i in range(0,n):
+    x_c[i] = np.cos((2 * i + 1) * np.pi / (2 * n))
+    
+f = runge(x)
+y_e = runge(x_e) # values for grid points for interpolation with equidistant grid points
+y_c = runge(x_c) # values for grid points for interpolation with Chebyshev grid points
+
+# Interpolation with equidistant grid points and evaluation of interpolated values at x
+a_e = np.diag(divided_differences(x_e, y_e))
+p_e = newton_interpolation(a_e, x_e, x)
+
+# Interpolation with Chebyshev grid points and evaluation of interpolated values at x
+a_c = np.diag(divided_differences(x_c, y_c))
+p_c = newton_interpolation(a_c, x_c, x)
+       
+       
+# Plotting of Runge and the two interpolated polynomials
+plt.rcParams['text.usetex'] = True
+
+plt.plot(x, f, label=r"$f(x) = \frac{1}{1 + 25 x^2}$")
+plt.plot(x, p_e, label=r"$p_n(x)$ equidistant")
+plt.plot(x, p_c, label=r"$p_n(x)$ Chebyshev")
+plt.plot([], [], ' ', label="$n = {}$".format(n))
+
+plt.title("A3)")
+plt.xlabel("x")
+plt.ylabel("y")
+plt.legend()
+
+plt.show()
+
+# braendel@math.tu-freiberg.de
diff --git a/uebung_02/main_matrix.c b/uebung_02/main_matrix.c
new file mode 100644
index 0000000..9380c05
--- /dev/null
+++ b/uebung_02/main_matrix.c
@@ -0,0 +1,64 @@
+#include <stdio.h>
+#include <stdlib.h>
+
+int compute(int N) {
+
+  int i_0, i_1;
+  // claim space
+  double **A = (double **)malloc(sizeof(double *) * N);
+  for (i_0 = 0; i_0 < N; i_0++) {
+    A[i_0] = (double *)malloc(sizeof(double) * N);
+  }
+  double *x = (double *)malloc(sizeof(double) * N);
+  double *y = (double *)malloc(sizeof(double) * N);
+  double *y_sol = (double *)malloc(sizeof(double) * N);
+
+  // fill matrix and vector
+  for (i_0 = 0; i_0 < N; i_0++) {
+    x[i_0] = i_0 + 1;
+    y_sol[i_0] = (i_0 + 1) * N;
+    for (i_1 = 0; i_1 < N; i_1++) {
+      A[i_0][i_1] = (i_0 + 1.0) / (i_1 + 1.0);
+    }
+  }
+
+  // for (i_0 = 0; i_0 < N; i_0++){
+  // 	printf("[ ");
+  // 	for(i_1 = 0; i_1 < N; i_1++){
+  // 		printf("%.3f ",A[i_0][i_1]);
+  // 	}
+  // 	printf("]");
+  // 	printf("[ %.1f ] = [ %.1f ][ %.1f ]\n",x[i_0],y[i_0],y_sol[i_0]);
+  // }
+
+  // compute matrix-vector product
+  for (i_0 = 0; i_0 < N; i_0++) {
+    y[i_0] = 0;
+    for (i_1 = 0; i_1 < N; i_1++) {
+      y[i_0] += A[i_0][i_1] * x[i_1];
+    }
+  }
+
+  // compare result to solution
+  double sum = 0.0;
+  for (i_0 = 0; i_0 < N; i_0++) {
+    sum += (y[i_0] - y_sol[i_0]) * (y[i_0] - y_sol[i_0]);
+  }
+
+  return sum;
+}
+
+int main(int argc, char *argv[]) {
+
+  int N;
+  if (argc != 2) {
+    N = 1000;
+  } else {
+    N = atoi(argv[1]); // Convert the argument to an integer
+  }
+
+  double err = compute(N);
+  printf("Error for N = %d: %.8f\n", N, err);
+
+  return 0;
+}
diff --git a/uebung_02/main_openmp.c b/uebung_02/main_openmp.c
new file mode 100644
index 0000000..92be7c1
--- /dev/null
+++ b/uebung_02/main_openmp.c
@@ -0,0 +1,19 @@
+#include <omp.h> // load Open-MP library
+#include <stdio.h>
+#include <stdlib.h>
+
+int main() {
+  int N = 5;
+  int num;
+
+#pragma omp parallel for private(num) // start Open-MP section
+  // here the program (1 thread) is split into multiple threads
+  // each thread has its own copy of i (loop) and num (private)
+  // all threads share N (by default, because defined outside)
+  for (int i = 0; i < N; i++) {
+    num = omp_get_thread_num();
+    printf("Thread %d does iteration %d\n", num, i);
+  }
+
+  return 0;
+}
diff --git a/uebung_02/matrix_mul b/uebung_02/matrix_mul
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diff --git a/uebung_02/openmp_hello b/uebung_02/openmp_hello
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index 0000000..00099eb
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diff --git a/uebung_04/exercise_01/exercise_01.c b/uebung_04/exercise_01/exercise_01.c
new file mode 100644
index 0000000..ca5fb6f
--- /dev/null
+++ b/uebung_04/exercise_01/exercise_01.c
@@ -0,0 +1,17 @@
+#include "mpi.h"
+#include <stdio.h>
+
+int main(int argc, char **argv) {
+  int rank, size, err, n;
+
+  MPI_Init(&argc, &argv);
+
+  MPI_Comm_size(MPI_COMM_WORLD, &size);
+  MPI_Comm_rank(MPI_COMM_WORLD, &rank);
+
+  printf("rank=%d size=%d\n", rank, size);
+
+  MPI_Finalize();
+
+  return 0;
+}
diff --git a/uebung_04/exercise_01/exercise_01.out b/uebung_04/exercise_01/exercise_01.out
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diff --git a/uebung_04/exercise_01/exercise_01.script b/uebung_04/exercise_01/exercise_01.script
new file mode 100644
index 0000000..649503a
--- /dev/null
+++ b/uebung_04/exercise_01/exercise_01.script
@@ -0,0 +1,13 @@
+#!/bin/bash
+
+## parameters
+#PBS -N uebung_04__exercise_01
+#PBS -q entry_teachingq
+#PBS -l select=1:ncpus=8:mpiprocs=8
+#PBS -l walltime=00:05:00
+
+## environment 
+cd ~/pwr/uebung_04/exercise_01
+
+## execute
+mpiexec -n 8 exercise_01.out
diff --git a/uebung_04/exercise_01/uebung_04__exercise_01.e662620 b/uebung_04/exercise_01/uebung_04__exercise_01.e662620
new file mode 100644
index 0000000..e69de29
diff --git a/uebung_04/exercise_01/uebung_04__exercise_01.o662620 b/uebung_04/exercise_01/uebung_04__exercise_01.o662620
new file mode 100644
index 0000000..89bfac5
--- /dev/null
+++ b/uebung_04/exercise_01/uebung_04__exercise_01.o662620
@@ -0,0 +1,8 @@
+rank=2 size=8
+rank=4 size=8
+rank=5 size=8
+rank=6 size=8
+rank=7 size=8
+rank=0 size=8
+rank=1 size=8
+rank=3 size=8
diff --git a/uebung_04/exercise_03/exercise_03.c b/uebung_04/exercise_03/exercise_03.c
new file mode 100644
index 0000000..2adcaf3
--- /dev/null
+++ b/uebung_04/exercise_03/exercise_03.c
@@ -0,0 +1,26 @@
+#include "mpi.h"
+#include <stdio.h>
+
+int main(int argc, char **argv)
+{
+	int rank, size, err, n;
+
+	MPI_Init(&argc, &argv);
+
+	MPI_Comm_size(MPI_COMM_WORLD,&size);
+	MPI_Comm_rank(MPI_COMM_WORLD,&rank);
+
+	printf("rank=%d size=%d\n", rank, size);
+
+	err = MPI_Barrier(MPI_COMM_WORLD);
+
+	n = (rank + 1) * 4711;
+
+	err = MPI_Bcast(&n, 1, MPI_INT, 1, MPI_COMM_WORLD);
+
+	printf("Received =%d\n", n);
+
+	MPI_Finalize();
+
+	return 0;
+}
diff --git a/uebung_04/exercise_03/exercise_03.out b/uebung_04/exercise_03/exercise_03.out
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diff --git a/uebung_04/exercise_03/exercise_03.script b/uebung_04/exercise_03/exercise_03.script
new file mode 100644
index 0000000..34e10b3
--- /dev/null
+++ b/uebung_04/exercise_03/exercise_03.script
@@ -0,0 +1,13 @@
+#!/bin/bash
+
+## parameters
+#PBS -N uebung_04__exercise_03
+#PBS -q entry_teachingq
+#PBS -l select=1:ncpus=8:mpiprocs=8
+#PBS -l walltime=00:05:00
+
+## environment 
+cd ~/pwr/uebung_04/exercise_03
+
+## execute
+mpiexec -n 8 exercise_03.out
diff --git a/uebung_04/exercise_05/exercise_05.c b/uebung_04/exercise_05/exercise_05.c
new file mode 100644
index 0000000..c236687
--- /dev/null
+++ b/uebung_04/exercise_05/exercise_05.c
@@ -0,0 +1,33 @@
+#include "mpi.h"
+#include <stdio.h>
+
+int main(int argc, char **argv) {
+  int rank, size, err, n, sum;
+
+  MPI_Init(&argc, &argv);
+
+  MPI_Comm_size(MPI_COMM_WORLD, &size);
+  MPI_Comm_rank(MPI_COMM_WORLD, &rank);
+
+  printf("rank=%d size=%d\n", rank, size);
+
+  n = rank + 1;
+
+  sum = 4710;
+
+  MPI_Barrier(MPI_COMM_WORLD);
+
+  MPI_Reduce(&n, &sum, 1, MPI_INT, MPI_SUM, 0, MPI_COMM_WORLD);
+  printf("Received in reduction=%d\n", sum);
+
+  MPI_Barrier(MPI_COMM_WORLD);
+
+  sum = 3710;
+
+  MPI_Allreduce(&n, &sum, 1, MPI_INT, MPI_SUM, MPI_COMM_WORLD);
+  printf("Received in allreduction =%d\n", sum);
+
+  MPI_Finalize();
+
+  return 0;
+}
diff --git a/uebung_04/exercise_05/exercise_05.out b/uebung_04/exercise_05/exercise_05.out
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