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ChrisUVA
Netherlands
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 Posted - 04/09/2005 : 2:44:26 PM
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Origin Version (Select Help-->About Origin): 7.0383
Operating System: WinXP
Hello there,
this is more a report about the very unpleasent discovery, that the interpretation of log(x) is different for the Advanced Fitting tool and a standard function window.
When fitting a certain group of data, I defined the following function (I now copy and paste directly from the entry fields):
y=P * 1/( 1+ w * ( log(x/c0) )^2 )
which gave me the following answers, and a nice matching curve.
P 0.25069 \(177)6.2211E-18
w 0.49039 \(177)4.1493E-17
c0 0.838 \(177)2.9356E-17
However, when I called a new Function window, and typed this very formula the curve did neither match the data nor the generated fitting funtion. To get it matching, I had to modify it to:
0.25069 * 1 / ( 1 + 2.6* log(x/0.838)^2 )
I tried the following:
0.25069 * 1/(1+ 0.49039*ln(x/0.838)^2 ) and indeed, that gave a perfect match.
To be really sure, I used the last function to generate a group of points, and used again the advanced fitting tool with the first function on it, and I got again the same result.
My conclusion is, that the Advanced fitting tool consideres log(x) as the natural logarithm, while the Function window considers it as the base 10 logarithm.
I could not see, if this problem is known or not. Neither did I find a remark in the help function.
Please comment.
regards,
ChB
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Mike Buess
USA
3037 Posts |
Posted - 04/09/2005 : 3:22:42 PM
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From the LabTalk programming guide... quote:
log(x)
The log(x) function returns the base 10 logarithm value of x.
Note: The LabTalk log function is based on 10 while the Origin C log function is based on e. The Origin C base 10 logarithmic function is log10.
The Advanced Fitting tool has an option for fitting with Origin C and you undoubtedly have that option checked.
Mike Buess
Origin WebRing Member |
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ChrisUVA
Netherlands
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Posted - 04/09/2005 : 3:47:56 PM
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indeed, origin C was checked true.
Where can I find the LabTalk Programming guide?
Note, that no documentation in physical form (i.e. books) is handed to the employees here.
thanks for the confirmation,
regards,
ChB |
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Mike Buess
USA
3037 Posts |
Posted - 04/09/2005 : 4:04:27 PM
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It's on your Help menu...
Help > Programming > LabTalk Language Reference
BTW, the quote I gave above was from the Origin 7.0 SR4 (v7.0552) programming guide. I don't know which service release v7.0383 is but you might consider updating to SR4.
Mike Buess
Origin WebRing Member |
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report Fitting function malinterpretation