Worked on ass4.

modsim/ass2/q4.c

@@ -4,6 +4,8 @@
 #include "func_ptr.h"
 
 #define EPSILON 1e-11
+#define MAX_STEPS 1000
+#define BISEC_STEPS 5
 
 double bisec_limited(func_ptr f, double left, double right, int max_steps) {
     int i;
@@ -23,10 +25,13 @@ double bisec_limited(func_ptr f, double left, double right, int max_steps) {
     return mid;
 }
 
-double newton(func_ptr f, func_ptr df, double x_start, int *steps) {
+double newton_raphson(func_ptr f, func_ptr df, double x_start, int *steps) {
     double x = x_start, last_x = x - 1;
 
     for( *steps = 0; x != last_x; (*steps)++ ) {
+        if( *steps == MAX_STEPS )
+            return NAN;
+
         last_x = x;
         x -= f(x) / df(x);
     }
@@ -34,6 +39,10 @@ double newton(func_ptr f, func_ptr df, double x_start, int *steps) {
     return x;
 }
 
+/*
+ * Manually define the functions and their derivatives.
+ */
+
 double f1(double x) {
     return x * x - x + 2;
 }
@@ -60,8 +69,12 @@ double df3(double x) {
 
 int main(void) {
     int steps;
+    double root;
 
-    printf("f1: %.11f (%d steps)\n", newton(&f2, &df2, -100, &steps), steps);
+    if( !isnan(root = newton_raphson(&f2, &df2, 1000000, &steps)) )
+        printf("f2: %.11f (%d steps)\n", root, steps);
+    else
+        printf("f2: could not find a root after %d steps\n", steps);
 
     return 0;
 }