sgolayfilt C语言实现

以下是一个简单的C语言实现sgolayfilt函数的示例代码：

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

void sgolayfilt(double *x, double *y, int nx, int order, int frame_len) {
    int i, j, k, n, nleft, nright;
    double sum;
    double *coeff;
    double *frame;
    
    if (frame_len % 2 == 0) {
        printf("Error: frame_len must be odd.\n");
        return;
    }
    
    if (frame_len < order + 1) {
        printf("Error: frame_len must be larger than order.\n");
        return;
    }
    
    coeff = (double *) malloc((order + 1) * sizeof(double));
    frame = (double *) malloc(frame_len * sizeof(double));
    
    nleft = frame_len / 2;
    nright = frame_len / 2;
    
    for (i = 0; i < nx; i++) {
        n = fmin(i, nx - i - 1);
        
        if (n < nleft) {
            nleft = n;
            nright = frame_len - nleft - 1;
        } else if (n < nright) {
            nright = n;
            nleft = frame_len - nright - 1;
        }
        
        for (j = 0; j < frame_len; j++) {
            k = i - nleft + j;
            
            if (k < 0) {
                frame[j] = x[0];
            } else if (k >= nx) {
                frame[j] = x[nx - 1];
            } else {
                frame[j] = x[k];
            }
        }
        
        for (j = 0; j <= order; j++) {
            sum = 0;
            
            for (k = -nleft; k <= nright; k++) {
                sum += pow(k, j);
            }
            
            coeff[j] = sum;
        }
        
        for (j = 0; j < frame_len; j++) {
            sum = 0;
            
            for (k = 0; k <= order; k++) {
                sum += coeff[k] * pow(j - nleft, k);
            }
            
            y[i] += sum * frame[j];
        }
        
        y[i] /= coeff[0];
    }
    
    free(coeff);
    free(frame);
}

在该实现中，我们使用了malloc函数动态分配内存，需要在使用完毕后使用free函数释放内存。该实现同样需要进行矩阵运算，因此在处理大型数据集时，可能会出现性能问题。