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)
Dim i As Long, y As Double
For i = 1 To n
    y = y + (-1 / Sqr(1 + (x / n * i) ^ 2)) * x / n
; ?$ o2 E% B: l2 Q$ |6 |7 K. xNext
Arccos = y
6 ~+ N2 i3 M4 J) B  c$ Y7 i) dEnd Function

! ^* [: _1 h: o# Y用的是Arccos的微分来算近似值，怎么不对？
5 @6 d' o4 @2 I' a1 N" F

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
    Case 1
        Arccos = 0
    Case -1
9 p5 z6 @' Z4 @        Arccos = pi
2 ]1 y- Z2 q7 {1 Q  f2 ?    Case -1 To 1
% g6 X' j7 }9 n- r. Y7 N6 w5 I        Dim dx As Double, y As Double, i As Long
5 G7 Q* @  V5 Z        dx = x / n
        For i = 1 To n
& m" {5 Z4 k' c- r1 K            y = y + (-1 / Sqr(1 - (dx * i + dx / 2) ^ 2)) * dx
0 f* k" j. ^$ W" R. ?& ~- }) P        Next
        Arccos = y + pi / 2
    Case Else
        '异常
0 w, B2 h# ~# z5 R    End Select
8 L/ N# y$ p4 ~End Function

3 J- I' A! z. W* H( q搞定了