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Precision in own functions

• To: mathgroup at smc.vnet.net
• Subject: [mg7746] Precision in own functions
• From: Yves Drexlmeier <drexl at mathematik.uni-kl.de>
• Date: Mon, 7 Jul 1997 04:41:19 -0400
• Organization: Dep. of Mathematics, Uni Kaiserslautern, Germany
• Sender: owner-wri-mathgroup at wolfram.com

Dear all,

I wrote a numerical funktion on Mathematika 2.2 and want to evaluate it with
 a higher precision then 16. Trying with SetPrecision and SetAccuracy made
 no better results (even not longer results i.e with more digits as it happens
 when you applie SetPrecision) 
Searching the error I found out that
 if you subtrackt two equal numbers with High Precision 
 say  N[1/3,40]-N[3/9,40] Mathematika gives 0. 10^-41 with a precision of 0.  

Is there a possibility to avoid this? For my intresst an exact 0 or 0 with 
the desired precision (40 in the example) would do it.
 
Yves Drexlmeier
drexl at mathematik.uni-kl.de