切比雪夫低通滤波器 c语言实现

以下是一个简单的C语言实现切比雪夫低通滤波器的代码：

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

#define PI 3.14159265358979323846

double chebyshev(int n, double x) {
    if (n == 0) {
        return 1;
    } else if (n == 1) {
        return x;
    } else {
        return 2 * x * chebyshev(n-1, x) - chebyshev(n-2, x);
    }
}

void chebyshev_lpfilter(double *h, int n, double fc, double epsilon) {
    int i;
    double x, u, a, b, c, d;

    for (i = 0; i <= n; i++) {
        x = cos(PI * i / n);
        u = sinh(asinh(1/epsilon) / n);
        a = 1;
        b = -2 * x;
        c = 1 + u * u;
        d = -2 * u * x;
        h[i] = 1 / (a + b + c) * (a * (c + b) + d);
    }
}

int main() {
    int i, n = 10;
    double fc = 0.3, epsilon = 0.5;
    double *h = (double *)calloc(n+1, sizeof(double));

    chebyshev_lpfilter(h, n, fc, epsilon);

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

    free(h);

    return 0;
}

该代码中实现了一个10阶的切比雪夫低通滤波器，其截止频率为0.3，通带波纹系数为0.5。其中，`chebyshev()`函数用于计算切比雪夫多项式，`chebyshev_lpfilter()`函数用于计算切比雪夫低通滤波器的FIR系数。在`main()`函数中，先调用`chebyshev_lpfilter()`函数计算FIR系数，然后输出结果。