VB中定义Arccos函数

游侠无极限

我是这样的：
) g) v1 K+ C1 _' `0 ?  wPrivate Function Arccos(x As Double, n As Long)
Dim i As Long, y As Double
) u4 \# n/ U5 m7 o; G$ y% L* H$ v7 \For i = 1 To n
    y = y + (-1 / Sqr(1 + (x / n * i) ^ 2)) * x / n
+ ?" h. Q1 J) W- e9 Z, ONext
+ [' S6 \7 Y- z% U5 AArccos = y
5 [1 u$ x* C" [9 @End Function
; T; x; b; z4 g
$ W5 B2 p4 Y7 R9 {+ _+ m! V' J用的是Arccos的微分来算近似值，怎么不对？

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
& o; z, l( y1 U, a. D, T    Case 1
        Arccos = 0
    Case -1
/ [5 T$ }" ^5 H, o0 \5 Q. g        Arccos = pi
- A1 H/ @! \0 l4 H( d" G+ T/ p    Case -1 To 1
        Dim dx As Double, y As Double, i As Long
        dx = x / n
, N6 }6 S1 U- E        For i = 1 To n
            y = y + (-1 / Sqr(1 - (dx * i + dx / 2) ^ 2)) * dx
        Next
$ C  i1 o, u8 }/ x$ D# j' D( ^) J        Arccos = y + pi / 2
    Case Else
! L. {& F/ X+ D  g& T8 h        '异常
' A# L$ E7 Y, U( C    End Select
End Function

搞定了