Implemented Euler method.

modsim/ass3/methods.c

@@ -20,18 +20,25 @@ occurs (overflow, NaN or such)
 
 int Euler(double t0, double t1, double dt, double *y0, double *y1, int N,
         f_ptr f, void *params) {
-    int i;
-    double slope[N];
+    int i, j, intervals = (t1 - t0) / dt;
+    double slope[N], t = t0;
 
-    if( f(t0, y0, slope, params) ) {
-        puts("Error calculating slope.");
-        return -1;
-    }
+    for( j = 0; j < N; j++ )
+        y1[j] = y0[j];
+
+    for( i = 0; i < intervals; i++ ) {
+        if( f(t, y0, slope, params) ) {
+            puts("Error calculating slope.");
+            return -1;
+        }
 
-    for( i = 0; i < N; i++ )
-        y1[i] = y0[i] + slope[i] * dt;
+        for( j = 0; j < N; j++ )
+            y1[j] = y1[j] + slope[j] * dt;
 
-    return (t1 - t0) > dt ? Euler(t0 + dt, t1, dt, y1, y1, N, f, params) : 0;
+        t = t0 + i * dt;
+    }
+
+    return 0;
 }
 /*
 int RungeKutta2(double t0, double t1, double dt, double *y0, double *y1, int N,

modsim/ass3/test.c

@@ -36,9 +36,9 @@ int f_cos(double t, double *y, double *dy, void *params) {
 }
 
 int main(void) {
-    double y0[1] = {.506}, y1[1];
+    double y0[1] = {.0}, y1[1];
 
-    if( Euler(-100.0, 10.0, 0.001, y0, y1, 1, &f_cos, NULL) ) {
+    if( Euler(.0, 10.0, .0001, y0, y1, 1, &f_cos, NULL) ) {
         puts("FAIL");
     } else {
         printf("y1: %f\n", *y1);