VB中定义Arccos函数

游侠无极限

我是这样的：
9 p3 R6 h/ a; O( _1 C- }9 mPrivate Function Arccos(x As Double, n As Long)
1 R. R7 N6 E* b+ PDim i As Long, y As Double
- @! y3 M' M, E9 K  b- \For i = 1 To n
3 Y8 c$ [  @0 i% o* m    y = y + (-1 / Sqr(1 + (x / n * i) ^ 2)) * x / n
* q3 i: y, a1 w, QNext
) [, E# E* E( P4 C4 F- CArccos = y
End Function
6 `* k" V; t% [4 B' _; P
' ~. d% V8 h. }4 P- H; ^- E- ~用的是Arccos的微分来算近似值，怎么不对？
9 {; d: W" g# d

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
& i9 Q- f! I& a  a& E, A" F) W" Q0 o    Select Case x
    Case 1
5 ]' u+ z, J3 w7 D! @2 @- `8 p( g        Arccos = 0
! q8 i7 r! w! s  L/ s6 x# |! y    Case -1
        Arccos = pi
    Case -1 To 1
        Dim dx As Double, y As Double, i As Long
        dx = x / n
        For i = 1 To n
7 `" S: \2 @2 y6 o2 v            y = y + (-1 / Sqr(1 - (dx * i + dx / 2) ^ 2)) * dx
3 v' ~/ c$ m; t  j* p8 }& A- r5 z        Next
3 T/ R9 p' F4 Q8 ^) `        Arccos = y + pi / 2
    Case Else
        '异常
    End Select
$ Y* F. j& A5 S1 Q, a  I9 DEnd Function

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