VB中定义Arccos函数

游侠无极限

我是这样的：
% N+ e0 K, ^1 D( g. j# k9 l/ q' |Private Function Arccos(x As Double, n As Long)
Dim i As Long, y As Double
For i = 1 To n
    y = y + (-1 / Sqr(1 + (x / n * i) ^ 2)) * x / n
( F) Q2 v$ ]  Q1 l! kNext
! v, d* c+ E2 z: @1 }Arccos = y
End Function

# m# e6 I8 g. o1 S用的是Arccos的微分来算近似值，怎么不对？
4 F2 E2 t' w2 i  a5 t* |

煎饼

公式对就没有问题拉

游侠无极限

Const pi As Double = 3.14159265359
Private Function Arccos(x As Double, n As Long) ' n 为函数精度，建议为100
    Select Case x
5 e, U9 S+ D6 w; ~. [* P    Case 1
        Arccos = 0
0 G& a4 L6 X- t6 r1 z  Z    Case -1
        Arccos = pi
    Case -1 To 1
) _% J* Y& h9 T+ \* @  F% G        Dim dx As Double, y As Double, i As Long
' e. D; Y% Z' }% O5 y: n1 l% r        dx = x / n
8 L$ ?3 N5 x: B3 k7 y4 L/ r0 B        For i = 1 To n
8 p* @7 `1 ^7 G: g3 N7 q/ W$ E1 z            y = y + (-1 / Sqr(1 - (dx * i + dx / 2) ^ 2)) * dx
, [1 y1 y+ {, R) c" H        Next
        Arccos = y + pi / 2
    Case Else
        '异常
6 o! s) I9 K8 D% r& h  w    End Select
End Function
- {. j' Y; s8 c0 ]8 ]
1 ^8 G$ r' a' A1 Z% v- }, B搞定了