SF [2159499] Full bigfloat precision for Gamma after the second call
Subject: SF [2159499] Full bigfloat precision for Gamma after the second call
From: Raymond Toy
Date: Tue, 14 Oct 2008 12:51:05 -0400
Raymond Toy wrote:
> Note that these differ quite a bit. Just need to track down what's
> happening here....
Some additional info. First, zot(z,fpprec) :=
bfloat(%pi*z/sin(%pi*z)); is enough to show the problem.
fpprec:64;
zot(bfloat(1/2),fpprec)$
:lisp bigfloat%pi
((BIGFLOAT SIMP 438)
557478319480384710099680955233841104245484663623488188587759156163931561121116157458028029845525521685028647707875576434771246873456
2)
:lisp (displa bigfloat%pi)
3.1415926535897932384626433832795028841971693993751058209749445923078164062862\
089986280348256812002485034480173261900300090541701233b0
So, for some reason, zot computed a 438-bit value of pi. But compare
this with the "true" value of pi:
fpprec:256; /* New value of pi computed */
3.1415926535897932384626433832795028841971693993751058209749445923078164062862\
089986280348253421170679821480865132823066470938446095505822317253594081284811\
174502841027019385211055596446229489549303819644288109756659334461284756482337\
The true value of pi (from www.joyofpi.com) is:
3.1415926535897932384626433832795028841971693993751058209749445923078164062862\
089986280348253421170679821480865132823066470938446095505822317253594081284811\
174502841027019385211055596446229489549303819644288109756659334461284756482337\
Note that 438 bit and 128 digit values of pi agree. But the 256 bit
value is quite a bit different, in the 128 digits!
Perhaps the computation of pi is somehow broken?
Ray