Chen Feng-Yi homework3

5_practice.c

@@ -2,39 +2,47 @@
 #include <stdlib.h>	// for memory allocation
 #include <time.h>	// for time calculation
 #include <math.h>	// for sine and cosine functions
+
 int main() {
 	// Declare all the variables
-	int k, n, N;
+	int u ,k, n, N;
 	double *x, *yr, *yi;
 	time_t t;
 
 	// Input the number N
-
-
+	printf("Please input a number N = ");
+	scanf("%d", &N);
 	// Locate the memory for x, yr, yi;
-
-	// Initial setting for x, for example, x[k] = k
-
-
-
-
+	x = (double *) malloc(N*sizeof(double));
+	yr = (double *) malloc(N*sizeof(double));
+    yi = (double *) malloc(N*sizeof(double));
+
+	// Initial setting for x, for example, x[k] = k, k=0..N-1 
+	for(k=0;k<N;++k) {
+		x[k] = k;
+	}
 	t = clock();	
+
 	// yr[n]+i*yi[n] = sum(exp(-i 2 Pi k n / N)*x[k], k=0..N-1), n=0..N-1 
-
-
-
-
-
-
-
+	for(n=0;n<N;n++) {
+		yr[n] = 0.0;
+		yi[n] = 0.0;
+		u = 2*M_PI*n/N;
+		for(k=0;k<N;++k) {
+			yr[n] += cos(u*k)*x[k];
+			yi[n] -= sin(u*k)*x[k];
+		}
+	}
+
 	// output the results
 	t = clock() - t;
 	printf("%d ms for discrete Fourier Transform of %d elements\n", t, N);
 
 	// free the memory located by x, yr, yi
-
+	free(x);
+	free(yr);
+	free(yi);	
 
 
 	return 100;
 }
-

readme.md

@@ -9,3 +9,4 @@
 3. 繼續寫下去 XD
 4. 大家來簽到吧
 5. 這是一個測試
+6. Binchiling! 峰