VB中定义Arccos函数

游侠无极限

我是这样的：
Private Function Arccos(x As Double, n As Long)
6 }& U% U7 }! w$ \Dim i As Long, y As Double
& t% }, [! {2 E% p1 fFor i = 1 To n
    y = y + (-1 / Sqr(1 + (x / n * i) ^ 2)) * x / n
Next
3 A9 e) t( E$ R0 N  O5 ^0 W' c+ [Arccos = y
/ o; a* q  C! bEnd Function
, B! ]. g* H6 h2 U8 Q1 g: l6 {
' S% k$ r$ O# P* T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
  V9 o/ N6 K; t; r# g    Case 1
        Arccos = 0
! v5 V" z! q* O% y1 O* {* t    Case -1
) d5 m8 J4 j: l1 z        Arccos = pi
    Case -1 To 1
        Dim dx As Double, y As Double, i As Long
        dx = x / n
        For i = 1 To n
            y = y + (-1 / Sqr(1 - (dx * i + dx / 2) ^ 2)) * dx
' B, _6 L4 q$ b* x' d$ B9 M1 B        Next
        Arccos = y + pi / 2
    Case Else
        '异常
$ w: b' R. b$ s    End Select
9 S* D+ G" ~4 d, AEnd Function
8 d& T/ ]( B5 K2 X1 C9 g
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