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[mathcad] RE: [mathcad]Re: Rounding up/down error
| [mathcad] RE: [mathcad]Re: Rounding up/down error |
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Author: Sander Lablans
Posted: Tue, 15 Jul 2003 11:01:08 +0200
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Well, the problem isn't that actually. I know about hidden digits. The fact
is that I DEFINED a variable with:
dp := 0.04425 N/mm^2
Therefore, I know that there are NO other digits after the 5. But for my
report, I have to use 4 digits instead of 5 (due to conformance throughout
the document). It was then that I found out about this strange occurence.
I do have to say that I think Chris does have the answer to this strange
behavior. I am no MathCad specialist, so I have to take his word for it that
MathCad uses a 52-bit normalised mantissa. But it would make sense.
In fact: if I change the value of 0.04425 to 0.05425 it is rounded to
0.0542, changing it to 0.06425, it gets rounded to 0.0643. If I change this
first non-zero digit from 0 to 9, I get a rather arbitrarily behavior of the
last digit, which would point to Chris' explanation.
Sander
-----Original Message-----
From: Markos E. Psarros />
Sent: dinsdag 15 juli 2003 10:28
To: Mathcad Discussion List
Subject: [mathcad] [mathcad]Re: Rounding up/down error
Dear Sander
Have you checked what is the ACTUAL number that underlies 0.04425?
If in 6 decimal points accuracy it was 0.044248 it would round in 5 digits
as 0.04425 (48 turns to 50) but if it was round to 4 digits it would give
0.0442 (because 248 rounds to 200 since it is NOT more than 250)!!
That for, check the result in 6 or even 8 digits accuracy and you'll see!
Markos
*********** REPLY SEPARATOR ***********
On 15/7/2003 at 9:12 pl Sander Lablans wrote:
[Edit] and now with attachment... [Edit]
Hello list,
I have been using a calculation with a number of 0.04425 N/mm^2.
However, I noticed a strange behavior when I modified the properties of a
result to show me 4 digits. Normally, it would then show me 0.0443 as a 5
always rounds up. However, as you can see in the attached mathcad-sheet,
MathCad decides that it does not want to show 0.0443, but 0.0442. I have
been playing with a few other numbers, but this is the only one I have
found. Can someone tell me, whether this is a bug in MathCad, or that there
is an option included in MathCad that makes sure that some results are
rounded to a different value? (Or perhaps someone else has encountered the
same rounding error somewhere else...)
Regards,
Sander Lablans
---------------------------------
NedTech Engineering B.V.
The Netherlands
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Dr. Markos E. Psarros
Ph.D. Civil Engineering
General Manager Software Imports and Sales
MP & Associates
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ATHENS 106 73
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