---
title: kml_float_spline_eval_deriv2
description: "这个函数返回插值函数对于给定点(x)的二阶微分。计算中使用插值对象spline，数据数组xarr，yarr以及加速器xacc。对于x在xarr的区间外，将返回报错信息。"
url: https://www.hikunpeng.com/document/detail/zh/hpchistory/hpckit/develop2400/kunpengaccel_kml_0505.html
sourcePath: /source/zh/hpchistory/hpckit/develop2400/kunpengaccel_kml_0505.html
indexId: f6814311c64d4ccb8bdafb4eddc120ffe1402a340c97c376a44b43979774e8fb67
---
# kml_float_spline_eval_deriv2

这个函数返回插值函数对于给定点(x)的二阶微分。计算中使用插值对象spline，数据数组xarr，yarr以及加速器xacc。对于x在xarr的区间外，将返回报错信息。

#### 接口定义

int kml_float_spline_eval_deriv2_e(const kml_float_spline *spline, float x, kml_spline_accel *a, float *d2)

float kml_float_spline_eval_deriv2(const kml_float_spline *spline, float x, kml_spline_accel *a)


#### 参数

| 参数名 | 类型 | 描述 | 输入/输出 |
| --- | --- | --- | --- |
| spline | kml\_float\_spline\* | 插值对象指针 | 输入 |
| x | float | 求解点x的值 | 输入 |
| y | float | 求解点y的值 | 输入 |
| a | kml\_spline\_accel \* | 加速器对象指针 | 输入 |


#### 依赖

#include "kml_spline.h"


#### 示例

```
const size_t xMin = 4;
const size_t xMax = 2048;
const size_t xSize = 4;
const float xValLo = 1;
const float xValHi = 2;
float xArr[4] = {1,1.33,1.67,2};
float* yArr = (float*)malloc(xSize * sizeof(float));
float x = 1;
float y = 0;
kml_float_spline *spline = kml_float_spline_alloc(kml_float_interp_cspline, xSize);
kml_interp_accel *xacc = kml_interp_accel_alloc();
kml_float_spline_init(spline, xSize, xArr, yArr);
y = kml_float_spline_eval_deriv2(spline, xArr, x, xacc);
kml_float_spline_free(spline);
kml_interp_accel_free(xacc);
free_if_not_null(xArr);
```