exp 10: init

Signed-off-by: Amneesh Singh <natto@weirdnatto.in>

10.c

@@ -0,0 +1,62 @@
+#include <math.h>
+#include <stdio.h>
+#include <stdlib.h>
+
+#define EPSILON 0.0000001
+
+double *eigen(double **matrix, int order) {
+  double mxerr = 0;
+  double *prev = calloc(order, sizeof(double));
+  *prev = 1;
+
+  do {
+    double *eigen = calloc(order, sizeof(double));
+
+    for (int i = 0; i < order; i++)
+      for (int j = 0; j < order; j++)
+        eigen[i] += matrix[i][j] * prev[j];
+
+    double mx = fabs(eigen[0]);
+    for (int i = 1; i < order; i++)
+      mx = fabs(eigen[i]) > mx ? fabs(eigen[i]) : mx;
+
+    for (int i = 0; i < order; i++)
+      eigen[i] /= mx;
+
+    double error[order];
+
+    for (int i = 0; i < order; i++)
+      error[i] = fabs(eigen[i] - prev[i]);
+
+    mxerr = error[0];
+    for (int i = 1; i < order; i++)
+      mxerr = error[i] > mxerr ? error[i] : mxerr;
+
+    free(prev);
+    prev = eigen;
+
+  } while (mxerr > EPSILON);
+
+  return prev;
+}
+
+int main() {
+  const int ORDER = 3;
+
+  double **matrix = malloc(ORDER * sizeof(double *));
+  for (int i = 0; i < ORDER; i++)
+    matrix[i] = malloc(ORDER * sizeof(double));
+
+  matrix[0][0] = 21, matrix[0][1] = -99, matrix[0][2] = 0;
+  matrix[1][0] = -12, matrix[1][1] = 64, matrix[1][2] = 0;
+  matrix[2][0] = 9, matrix[2][1] = -0.5, matrix[2][2] = 4;
+
+  double *egn = eigen(matrix, ORDER);
+
+  for (int i = 0; i < ORDER; i++) {
+    printf("%lf ", egn[i]);
+    free(matrix[i]);
+  }
+  free(egn);
+  free(matrix);
+}