Re: [BLACKBOX] Math.Pi (was: CONSTant expressions)

From: Campbell, Robert D (SELEX) (UK Edinburgh) <"Campbell,>
Date: Mon, 21 Jan 2008 10:35:45 -0000

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Chris

>> I first noticed pi # Pi about 10 years ago!
>> I vaguely remember investigating this at the time and discovering
that Pi was more
>> accurate than pi. But my memory could be playing me tricks.


In the code below a and b are approximations to
0.00000890891020676153735661672049711580283060062489... .

The error in a is about 1.22464023514E-016,
which is consistent with pi being correct to about 64 bits.

The error in b is about -5.08219768353E-020,
which is consistent with Math.Pi being correct to about 80 bits,
and the subtraction being done to 80 bits.


  CONST
    ratPi = 3.1416015625; (* 3217 / 1024, Exactly *)
  VAR
    a, b, pi : REAL;
  BEGIN
    pi := Math.Pi ();
    a := ratPi - pi;
    b := ratPi - Math.Pi ();


Cheers

Robert

SELEX Sensors and Airborne Systems Limited
Registered Office: Sigma House, Christopher Martin Road, Basildon, Essex SS14 3EL
A company registered in England & Wales. Company no. 02426132
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Received on Mon Jan 21 2008 - 11:35:45 UTC