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)
) h# y* s8 Z. {1 w5 zDim i As Long, y As Double
" n; W* x7 F- Y; Q( Y9 EFor i = 1 To n
, h0 D- Y% b3 f+ [2 \" [/ T    y = y + (-1 / Sqr(1 + (x / n * i) ^ 2)) * x / n
Next
Arccos = y
, f! i( R2 I' k& n$ V9 }6 f! T7 |End Function

( h7 y5 {! e! Z- [7 _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
0 \  H% W& R/ h+ }( J- |/ E    Case 1
: U9 c& b& h" [0 M# d0 Z! M        Arccos = 0
    Case -1
7 @1 t0 I" X6 i) ^        Arccos = pi
/ l- E2 _3 E/ r4 C% S& E    Case -1 To 1
. [( y) \+ O1 W& a& j        Dim dx As Double, y As Double, i As Long
        dx = x / n
        For i = 1 To n
- t9 c% {# g8 h" b, R" e2 t            y = y + (-1 / Sqr(1 - (dx * i + dx / 2) ^ 2)) * dx
        Next
1 X( G) u( o  |0 a, O1 J        Arccos = y + pi / 2
1 \3 _& z' T4 \1 m9 g. q9 j    Case Else
        '异常
    End Select
End Function
9 @! h. x% O( [4 R! V& B
; z6 n" N7 F( P& b1 D' _! ]5 J1 J2 y搞定了