ModSim ass3: Added early implementation of Euler method.

modsim/ass3/.gitignore

+test

modsim/ass3/Makefile

@@ -4,11 +4,11 @@ LFLAGS=-lm
 
 all: test
 
-test: test.o methods.o
+test: test.c methods.c
 	$(CC) $(CFLAGS) $(LFLAGS) -o $@ $^
 
-%.o: %.c
-	$(CC) $(CFLAGS) $(LFLAGS) -o $@ $^
+#%.o: %.c
+#	$(CC) $(CFLAGS) $(LFLAGS) -o $@ $^
 
 clean:
 	rm *.o test

modsim/ass3/methods.c

@@ -20,15 +20,20 @@ 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, steps = (int)((t1 - t0) / dt + .5);
-
-    for( i = 0; i < N; i++ ) {
+    int i;
+    double slope[N];
 
+    if( f(t0, y0, slope, params) ) {
+        puts("Error calculating slope.");
+        return -1;
     }
 
-    return 0;
-}
+    for( i = 0; i < N; i++ )
+        y1[i] = y0[i] + slope[i] * dt;
 
+    return (t1 - t0) > dt ? Euler(t0 + dt, t1, dt, y1, y1, N, f, params) : 0;
+}
+/*
 int RungeKutta2(double t0, double t1, double dt, double *y0, double *y1, int N,
         f_ptr f, void *params) {
 
@@ -39,4 +44,4 @@ int RungeKutta4(double t0, double t1, double dt, double *y0, double *y1, int N,
         f_ptr f, void *params)
 
     return 0;
-}
+}*/

modsim/ass3/methods.h

@@ -2,9 +2,10 @@ typedef int (*f_ptr)(double t, double *y, double *dy, void *params);
 
 int Euler(double t0, double t1, double dt, double *y0, double *y1, int N,
     f_ptr f, void *params);
-
+/*
 int RungeKutta2(double t0, double t1, double dt, double *y0, double *y1, int N,
     f_ptr f, void *params);
 
 int RungeKutta4(double t0, double t1, double dt, double *y0, double *y1, int N,
     f_ptr f, void *params);
+    */

modsim/ass3/test.c

 #include <stdlib.h>
 #include <stdio.h>
+#include <math.h>
 #include "methods.h"
 
 int f_test_1(double t, double *y, double *dy, void *params) {
     *dy = 1.0;
 
-    return 1;
+    return 0;
 }
 
-int f_test_2(double t, double *y, double *dy, void *params) {
-    double result = *y;
-
-    if( isnan(result) ) {
+int f_test_3(double t, double *y, double *dy, void *params) {
+    if( isnan(*y) ) {
         return -1;
     } else {
-        *dy = result;
+        *dy = *y;
         return 0;
     }
 }
 
-int f_test_3(double t, double *y, double *dy, void *params) {
+int f_test_4(double t, double *y, double *dy, void *params) {
     double result = *y * *y;
 
     if( isnan(result) ) {
@@ -30,8 +29,20 @@ int f_test_3(double t, double *y, double *dy, void *params) {
     }
 }
 
+int f_cos(double t, double *y, double *dy, void *params) {
+    *dy = cos(t);
+
+    return 0;
+}
+
 int main(void) {
+    double y0[1] = {.506}, y1[1];
 
+    if( Euler(-100.0, 10.0, 0.001, y0, y1, 1, &f_cos, NULL) ) {
+        puts("FAIL");
+    } else {
+        printf("y1: %f\n", *y1);
+    }
 
     return 0;
 }