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MathGroup Archive 2002

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Re: Accuracy and Precision

  • To: mathgroup at smc.vnet.net
  • Subject: [mg36903] Re: Accuracy and Precision
  • From: pkosta2002 at yahoo.com (Peter Kosta)
  • Date: Tue, 1 Oct 2002 04:45:51 -0400 (EDT)
  • References: <an8stl$6tq$1@smc.vnet.net>
  • Sender: owner-wri-mathgroup at wolfram.com

Thanks to all who adviced me on the correct use of 
SetAccuracy. However, I still don't understand why 
the order in which we set the accuracies for f, a, 
and b matters.

In[1]:=
f = SetAccuracy[333.75*b^6 + a^2*(11*a^2*b^2 - b^6 - 
       121*b^4 - 2) + 5.5*b^8 + a/(2*b), Infinity]; 
a = SetAccuracy[77617., Infinity]; 
b = SetAccuracy[33096., Infinity]; 

In[4]:=
f

Out[4]=
-(54767/66192)

In[5]:=
f = SetAccuracy[333.75*b^6 + a^2*(11*a^2*b^2 - b^6 - 
       121*b^4 - 2) + 5.5*b^8 + a/(2*b), Infinity] 

Out[5]=
1180591620717411303424

Similarily:

In[1]:=
f = SetAccuracy[333.75*b^6 + a^2*(11*a^2*b^2 - b^6 - 
       121*b^4 - 2) + 5.5*b^8 + a/(2*b), 50]; 
a = SetAccuracy[77617., 100]; 
b = SetAccuracy[33096., 100]; 

In[4]:=
f

Out[4]=
-0.8273960599468212641107299556`11.4133

In[5]:=
f = SetAccuracy[333.75*b^6 + a^2*(11*a^2*b^2 - b^6 - 
       121*b^4 - 2) + 5.5*b^8 + a/(2*b), 100]; 

Out[5]=
1.180591620717411303424`121.0721*^21

-PK


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