Added animated plotting program.

modsim/ass4_taddeus/vibstring/.gitignore

 seq
+seq2

modsim/ass4_taddeus/vibstring/Makefile

@@ -2,8 +2,8 @@ CC=gcc
 CFLAGS=-Wall -Wextra -pedantic -std=c99 -O0 -D_GNU_SOURCE
 LDFLAGS=-lm
 
-all: seq
-seq: seq.o
+all: seq2
+seq2: seq2.o
 
 clean:
 	rm -vf *.o vibstring

modsim/ass4_taddeus/vibstring/draw.py

+#!/usr/bin/env python
+from sys import stdin
+from pylab import figure, plot, axis, draw, ion, clf
+from time import sleep
+
+# Collect data
+y = []
+lines = stdin.readlines()
+x = map(float, lines[0].split(' '))
+for line in lines[1:]:
+    y += [map(float, line.split(' '))]
+
+# Find axis maxima
+max_y = max([max(map(abs, y[i])) for i in range(len(y))])
+ranges = [0, max(x), -max_y, max_y]
+
+# Plot data in animation
+try:
+    ion()
+    figure(1)
+    for i in range(len(y)):
+        clf()
+        plot(x, y[i], '-')
+        axis(ranges)
+        draw()
+        sleep(.01)
+except KeyboardInterrupt:
+    print 'Quitting...'

modsim/ass4_taddeus/vibstring/plot.py

 #!/usr/bin/env python
 from sys import argv, stdin
-from pylab import figure, plot, subplot, show, savefig, legend
+from pylab import figure, plot, subplot, show, savefig, legend, axis
 from time import sleep
 
 # Collect data
@@ -16,7 +16,7 @@ figure(len(t))
 for i in range(len(t)):
     subplot(2, 5, i + 1)
     plot(y[i][0], y[i][1], 'x-', label='t = %.3f' % t[i])
-    #legend()
+    axis([0, 1, -1, 1])
 if len(argv) == 2:
     savefig(argv[1])
 show()

modsim/ass4_taddeus/vibstring/seq2.c

+#include <stdlib.h>
+#include <stdio.h>
+#include <string.h>
+#include <math.h>
+
+double **create_y(int steps) {
+    double **y = (double **)malloc(3 * sizeof(double *));
+    int i;
+
+    if( y == NULL ) {
+        puts("Error: could not allocate memory.");
+        exit(EXIT_FAILURE);
+    }
+
+    for( i = 0; i < 3; i++ )
+        y[i] = (double *)malloc(steps * sizeof(double));
+
+    return y;
+}
+
+/*
+ *
+ */
+void init_sinus(double **y, int steps, double l, double dx, double n) {
+    for( int i = 0; i < steps; i++ )
+        y[0][i] = sin(n * M_PI * i * dx / l);
+
+    // The string is attached at both ends
+    y[2][0] = y[1][0] = y[0][0];
+    y[2][steps - 1] = y[1][steps - 1] = y[0][steps - 1];
+}
+
+/*
+ *
+ */
+void init_plucked(double **y, int steps, double l, double dx, double xp) {
+    double x;
+
+    for( int i = 0; i < steps; i++ ) {
+        x = i * dx;
+        y[0][i] = x < xp ? x / xp : (l - x) / (l - xp);
+    }
+
+    // The string is attached at both ends
+    y[2][0] = y[1][0] = y[0][0];
+    y[2][steps - 1] = y[1][steps - 1] = y[0][steps - 1];
+}
+
+#define VERBOSE
+
+#ifdef VERBOSE
+#define PRINT_FORMAT "%e"
+
+void print(double *y, int string_steps) {
+    for( int i = 0; i < string_steps; i++ ) {
+        if( i )
+            printf(" ");
+
+        printf(PRINT_FORMAT, y[i]);
+    }
+
+    puts("");
+}
+#endif
+
+/*
+ *
+ */
+void iterate(double **y, int string_steps, double dx, int calc_steps,
+        int print_resolution, double tau) {
+    double x;
+    int i, t, prev = 0, current = 1, next = 2;
+
+    // Calculate the position over the entire string at time dt using the
+    // position at t = 0 and the information that y(x, -dt) == y(x, dt)
+    for( i = 1; i < string_steps - 1; i++ ) {
+        x = i * dx;
+        y[1][i] = y[0][i] + .5 * tau * tau * (y[0][i-1] - 2 * y[0][i]
+                  + y[0][i+1]);
+    }
+
+    #ifdef VERBOSE
+    // Print x values (which are the same for every y-series)
+    for( i = 0; i < string_steps; i++ ) {
+        if( i )
+            printf(" ");
+
+        printf(PRINT_FORMAT, i * dx);
+    }
+
+    puts("");
+
+    // Print init states
+    print(y[prev], string_steps);
+
+    if( print_resolution == 1 )
+        print(y[current], string_steps);
+    #endif
+
+    // Iterate over the length of the string for each time interval step
+    for( t = 2; t < calc_steps; t++ ) {
+        for( i = 1; i < string_steps - 1; i++ ) {
+            y[next][i] = 2 * y[current][i] - y[prev][i] + tau * tau
+                * (y[current][i-1] - 2 * y[current][i] + y[current][i+1]);
+        }
+
+        #ifdef VERBOSE
+        if( !(t % print_resolution) )
+            print(y[next], string_steps);
+        #endif
+
+        prev = current;
+        current = next;
+        next = (next + 1) % 3;
+    }
+}
+
+int main(int argc, const char **argv) {
+    int x_steps, calc_steps, i, print_resolution;
+    void (*init_method)(double **, int, double, double, double);
+    double **y, l, dx, tau, constant;
+
+    if( argc < 8 ) {
+        printf("Usage: %s INIT_METHOD CALCULATION_STEPS PRINT_RESOLUTION LENGTH"
+               " DX TAU N|XP\n", argv[0]);
+        return EXIT_FAILURE;
+    }
+
+    if( !strcmp(argv[1], "sinus") ) {
+        init_method = init_sinus;
+    } else if( !strcmp(argv[1], "plucked") ) {
+        init_method = init_plucked;
+    } else {
+        printf("Unknown initialization method '%s'.\n", argv[1]);
+        return EXIT_FAILURE;
+    }
+
+    calc_steps = atoi(argv[2]);
+    print_resolution = atoi(argv[3]);
+    l = atof(argv[4]);
+    dx = atof(argv[5]);
+    tau = atof(argv[6]);
+    constant = atof(argv[7]);
+
+    x_steps = (int)ceil(l / dx);
+    y = create_y(x_steps);
+    (*init_method)(y, x_steps, l, dx, constant);
+    iterate(y, x_steps, dx, calc_steps, print_resolution, tau);
+
+    // Free allocated memory
+    for( i = 0; i < 3; i++ )
+        free(y[i]);
+
+    free(y);
+
+    return EXIT_SUCCESS;
+}