Text 344, 99 rader
Skriven 2005-03-13 21:17:00 av "basil Fawlty" <basil_faw (1:278/230)
Ärende: Re: Newbie Help: Simple VB Program to Compute Volume of Cyli
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Steve, out of my own curiosity, where does it become important to split
hairs like this with PI?  What industry would need this to solve a problem
needing highly a precise PI value?  BTW, I never knew PI could spark up such
an interest.

"Steve Gerrard" <mynamehere@comcast.net> wrote in message
news:3OGdnbdEL8KhPqnfRVn-rA@comcast.com...
>
> "Rick Rothstein" <rickNOSPAMnews@NOSPAMcomcast.net> wrote in message
> news:eY-dncPBuqGhBqnfRVn-uQ@comcast.com...
>>> > I find it just as easy to remember 4 * Atn(1)
>>>
>>> But you can't assign that to a Const in VB. Also, I would think the
>>> function call is slower than a single division operation. Of course,
>>> 4*Atn(1) is more accurate though.
>>
>> Also, if you need to work out a "quick" calculation on paper (no
>> computer, no calculator available), being able to remember that fraction
>> will prove quite useful and quite easy to make use of.
>>
>
> Here is a little program I just ran for fun, to find the best integer
> pairs for approximating PI. If you can come up with a handy mnemonic, you
> could use 1881244168 / 598818617 to get very close. The precision is
> around E-18.
>
> It appears to be better than just hard coding PI as a constant double. I
> get fuzzy on the precision thing with doubles, I think the processor
> carries more precision (10 bytes instead of 8?). I think the above
> division would be faster than the trig function 4 * Atn(1), unless the
> processor has Atn(1) stored somewhere.
>
> 'two buttons, one list box, one text box
>
> Option Explicit
>
> Private mGo As Boolean
>
> Private Sub Command1_Click()
>    On Error Resume Next
>
>    mGo = True
>    Call FindPiPair
>
>    If Err.Number <> 0 Then
>        mGo = False
>        MsgBox Err.Description
>    End If
>
> End Sub
>
> Private Sub Command2_Click()
>    mGo = False
> End Sub
>
> Private Sub Form_QueryUnload(Cancel As Integer, UnloadMode As Integer)
>    mGo = False
> End Sub
>
> Private Sub FindPiPair()
>    Static nBot As Long
>    Static dBest As Double
>    Dim nTop As Long
>    Dim dDiff As Double
>    Dim strOut As String
>
>    While mGo
>
>        nBot = nBot + 1
>        nTop = 4 * Atn(1) * nBot
>        dDiff = 4 * Atn(1) - (nTop / nBot)
>
>        If nBot = 1 Or Abs(dDiff) < dBest Then
>            dBest = Abs(dDiff)
>            strOut = nTop & " / " & nBot & " = " & (nTop / nBot)
>            strOut = strOut & vbTab & "    (" & dDiff & ")"
>            List1.AddItem strOut
>            List1.ListIndex = List1.NewIndex
>            DoEvents
>
>        ElseIf nBot Mod 10000 = 0 Then
>            Text1.Text = nBot
>            DoEvents
>        End If
>
>    Wend
>
> End Sub
>
>
>




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