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MathGroup Archive 2004

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Beware of adding 0.0

  • To: mathgroup at smc.vnet.net
  • Subject: [mg50206] Beware of adding 0.0
  • From: "paul" <paul_tan at aoI.com>
  • Date: Fri, 20 Aug 2004 04:58:00 -0400 (EDT)
  • Sender: owner-wri-mathgroup at wolfram.com

In Mathematica 5.0, I get a very strange result when I add 0.0 to a number,
why is this?  See below:

p = SetPrecision[314159265358979323, 25]
q = SetPrecision[314159265358979323., 25]
r = SetPrecision[314159265358979323.00000000000000000000, 25]
s = SetPrecision[p + 0.0, 25]
{p == q, q == r, r == s, r == p}
{Tan[s], N[Tan[p]], Tan[q], Tan[r]}


\!\(3.14159265358979323`25.*^17\)
Out[47]=
\!\(3.14159265358979323`25.*^17\)
Out[48]=
\!\(3.14159265358979323`25.*^17\)
Out[49]=
\!\(3.14159265358979328`25.*^17\)   *****NOTICE the 28 instead of 23 at the
end, why does this happen? *******
Out[50]=
{True, True, False, True}
Out[51]=
{1.599808, -1.12979, -1.1297927, -1.1297927}


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