用c语言实现db3小波

DB3小波是一种离散小波变换（DWT）中的小波基，它的离散小波变换函数可以用C语言实现。下面是一个简单的例子：

#include <stdio.h>
#include <stdlib.h>
#include <math.h>

#define N 8

double h[] = {0.4829629131445341, 0.8365163037378079, 0.2241438680420134, -0.1294095225512603, -0.4829629131445341, 0.8365163037378079, -0.2241438680420134, -0.1294095225512603};
double g[] = {-0.1294095225512603, 0.2241438680420134, 0.8365163037378079, 0.4829629131445341, -0.1294095225512603, -0.2241438680420134, 0.8365163037378079, -0.4829629131445341};

void dwt(double *x)
{
    int n = N;
    double temp[n];
    int i, j, k;

    for (i = 0; i < N; i++) {
        temp[i] = 0.0;
        for (j = 0, k = i; j < N; j++, k = (k + 1) % N) {
            temp[i] += h[j] * x[k];
        }
    }

    for (i = 0; i < N; i++) {
        x[i] = temp[i];
    }

    for (i = 0; i < N; i++) {
        temp[i] = 0.0;
        for (j = 0, k = i; j < N; j++, k = (k + 1) % N) {
            temp[i] += g[j] * x[k];
        }
    }

    for (i = 0; i < N; i++) {
        x[i] = temp[i];
    }
}

int main()
{
    double x[] = {1.0, 2.0, 3.0, 4.0, 5.0, 6.0, 7.0, 8.0};
    int i;

    printf("Input: ");
    for (i = 0; i < N; i++) {
        printf("%f ", x[i]);
    }
    printf("\n");

    dwt(x);

    printf("Output: ");
    for (i = 0; i < N; i++) {
        printf("%f ", x[i]);
    }
    printf("\n");

    return 0;
}

这个例子实现了一个8个点的DB3小波变换，其中h和g是DB3小波的滤波器系数。通过调用dwt函数，可以对输入信号进行DB3小波变换。