RE: [ECOS] One question.

[<Zhao.Green@inventec-inc.com>]

Dear Sir:
	Sure, if I try to less precision in output. The result can be round back to 0.1.
But if  the dnum1 = 0.00000000001 , dnum2 = dnum1.
Result = dnum1+dnum2 
The result is 0.00000000002
This amaze me.

When dnum1  = 0.00000000001, the register show this value is 9.9999999999999994e-12.



BR
Green



-----Original Message-----
From: ecos-discuss-owner@ecos.sourceware.org [mailto:ecos-discuss-owner@ecos.sourceware.org] On Behalf Of Paul D. DeRocco
Sent: Wednesday, May 31, 2006 2:29 PM
To: eCos Discuss
Subject: RE: [ECOS] One question.

> From: Zhao.Green@inventec-inc.com
>
> 	I use the ecos package , and I found the double type question Double 
> dnum1 = 1234567.1 Double dnum2 = 1234567 Double result = 0 ;
>
> Result = dnum1-dnum2 ;
>
> The result is 0.10000000009
>
> Anybody know how to solve this question?

0.1 can't be represented exactly in binary, so there's an inevitable roundoff error. Sometimes these errors are hidden by the implementation of the binary to decimal conversion used in printing out the answer, but sometimes not. I don't know if you're using printf in C, or << in C++, but you might try requesting less precision in the output, to see if that rounds the result back to 0.1.

--

Ciao,               Paul D. DeRocco
Paul                mailto:pderocco@ix.netcom.com


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