c++ 自己实现matlab的filter函数

实现MATLAB的filter函数需要使用差分方程，并且需要实现FIR和IIR两种滤波器类型。下面是一个使用C++实现MATLAB的filter函数的示例代码：

#include <iostream>
#include <vector>

using namespace std;

// FIR滤波器
vector<double> fir_filter(vector<double> x, vector<double> b)
{
    int n = x.size();
    int m = b.size();
    vector<double> y(n);

    for (int i = 0; i < n; i++) {
        y[i] = 0;
        for (int j = 0; j < m; j++) {
            if (i - j >= 0) {
                y[i] += b[j] * x[i-j];
            }
        }
    }

    return y;
}

// IIR滤波器
vector<double> iir_filter(vector<double> x, vector<double> a, vector<double> b)
{
    int n = x.size();
    int m = a.size();
    int l = b.size();
    vector<double> y(n);

    for (int i = 0; i < n; i++) {
        y[i] = 0;
        for (int j = 0; j < l; j++) {
            if (i - j >= 0) {
                y[i] += b[j] * x[i-j];
            }
        }
        for (int k = 1; k < m; k++) {
            if (i - k >= 0) {
                y[i] -= a[k] * y[i-k];
            }
        }
        y[i] /= a[0];
    }

    return y;
}

// filter函数
vector<double> filter(vector<double> b, vector<double> a, vector<double> x)
{
    vector<double> y;

    if (b.size() > a.size()) {
        y = fir_filter(x, b);
    } else {
        y = iir_filter(x, a, b);
    }

    return y;
}

// 示例代码
int main()
{
    vector<double> x = {1, 2, 3, 4, 5};
    vector<double> b = {1, 2, 3, 2, 1};
    vector<double> a = {1, -0.5};

    vector<double> y = filter(b, a, x);

    for (int i = 0; i < y.size(); i++) {
        cout << y[i] << " ";
    }
    cout << endl;

    return 0;
}

在示例代码中，我们实现了FIR和IIR两种滤波器类型，并通过filter函数实现了MATLAB的filter函数。你可以将你自己的滤波器系数和输入信号传递给filter函数来获得滤波后的输出信号。