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)
/ Q) `5 f+ i4 A+ Q2 nDim i As Long, y As Double
, x; Z: Y* x  l. W9 v5 T2 x- G" @For i = 1 To n
4 s6 S* h1 e( b3 _    y = y + (-1 / Sqr(1 + (x / n * i) ^ 2)) * x / n
Next
Arccos = y
8 s: j0 d' [. t) s* _End Function
1 m8 k; Z) G* b" a* h; n0 K2 F
4 V" G( _( W' Q用的是Arccos的微分来算近似值，怎么不对？
( a+ P: A+ y  L% I. x

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
( U6 x- l; F8 d& s3 U5 P; z9 n    Case 1
6 V  w4 D+ k) [        Arccos = 0
    Case -1
        Arccos = pi
# k/ V# g1 _4 F9 C    Case -1 To 1
2 Z- Z! i  s  C4 O        Dim dx As Double, y As Double, i As Long
        dx = x / n
8 F* C, q4 {( ]        For i = 1 To n
' l9 w3 M" [. ^            y = y + (-1 / Sqr(1 - (dx * i + dx / 2) ^ 2)) * dx
        Next
        Arccos = y + pi / 2
    Case Else
8 ^! f+ |9 n( E+ C        '异常
    End Select
& D" D/ ^( D. ~# B) d& AEnd Function
& j! e: P# e0 C+ O2 D  ?
3 K8 b* s# P5 P, {2 s# G" H搞定了