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SteffenG
Germany
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 Posted - 06/28/2005 : 06:23:59 AM
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Origin Version (7.5G SR5):
Operating System: Win XP pro
Hi,
in my current work I want to fit some data with a simple expression.
The expression is y=A+B*log(x) - really simple, I know.
If i use the NLSF-tool I can specify new fitting function and I can also check a little box to use Origin-C to compile the function for speed improvements. But with checking the box the fitting results were changed. The parameter A was equal to the unchecked version of results but the parameter B changed from unchecked to checked version of results with a factor of 2.30. So there seems to be a difference between the two results of parameter B of ln(10).
For my understanding the log-function without checking is the logarithm to base 10 but if I check the Origin-C option the log-function is the logarithm to base e (in other words it is ln).
My suggestion is that a warning should come up if a function with log in it is compiled in Origin-C to inform the user about the change of the mathematical meaning. Or the Origin-C-Code should be able to handle the log as log10 and not ln.
Kind regards,
Steffen |
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Mike
USA
357 Posts |
Posted - 06/28/2005 : 09:50:05 AM
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Hi Steffen,
You are correct, and -- YES, ABSOLUTELY -- we should warn NLSF users of this. Documentation of this can be found in the Origin C Language Reference section of the Programming Help file (Help:Programming) under the the topic Function: ln, but the average NLSF user wouldn't think to look here.
Thank your for pointing this problem out to us. We will enter an item in our bug-tracking database, straight away. Sorry for the confusion.
P.S. I should say that in OC, logarithm of base 10 is log10( )
P.P.S. I entered a note under database item = QA 7085 and referenced your forum post.
Mike
OriginLab
Edited by - Mike on 06/28/2005 09:54:35 AM
Edited by - Mike on 06/28/2005 10:55:00 AM |
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SteffenG
Germany
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Posted - 06/29/2005 : 05:12:57 AM
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Hi Mike,
thanks for your reply. If this issue will be fixed everything will be fine.
BTW: I am highly pleased to work with Origin. It is a very good program and if you do a Mac OS X version my satisfaction will be much higher ;-) I know up to now OriginLab said NO to a Mac OS X version but with the next generation of Intel-based Macs I hope OriginLab will change their opinion.
Best regards,
Steffen |
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greg
USA
1379 Posts |
Posted - 06/29/2005 : 10:17:54 AM
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Please understand that this is NOT a bug and nothing will be fixed. This is standard ANSI C and users who are transitioning from LabTalk to OriginC need to be aware of the differences.
Mike's point was that we should try to warn users at appropriate times, which we already try to do with comments in the NLSF fitter (which you will not see unless you scroll up in Code Builder view).
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Bug: Log() isn't always log10(), it's also ln()