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Tmlcky
Italy
4 Posts |
 Posted - 07/12/2013 : 10:51:02 AM
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Origin Ver. and Service Release (Select Help-->About Origin): Origin Pro 9.0.0 (32bit) SR2
Operating System: Windows XP virtualized on Fusion 2.0.8 (iMac 21; MAC OS X 10.6.8)
Dear all,
I am a very beginner user of Origin Pro (and not skilled in math).
I got data of a photosynthetic parameter (ETR) in response to light (PAR).
I wanted to fit my data to ExpDec1 function: y = A1*exp(-x/t1) + y0.
Fitting converged. Then I wanted to constrain the fitted curve to pass through the origin, as with PAR=0 (no light), ETR should also be zero.
So I added this constraint to the Code/Constraints window:
y = A1*exp(-0/t1) + y0 = 0
I also tried:
0 = A1*exp(-0/t1) + y0
and
A1*exp(-0/t1) + y0 = 0
In any case, I got this message:
Error in constraints - Please check syntax such as parameter names and operators.
Would you please help me?
Best regards,
Pasquale Giorio
CNR-ISAFOM
via Patacca, 85
80056- Ercolano (NA),
Italia
tel: +39 081 5746606 (int. 230, 224 or 231)
fax: +39 081 7718045
Email: pasquale.giorio@cnr.it |
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malgoska
Poland
36 Posts |
Posted - 07/12/2013 : 11:25:37 AM
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If you want to make the curve pass through zero, you must simply put y0=-1 (as exp(0)=1).
Regards |
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Tmlcky
Italy
4 Posts |
Posted - 07/12/2013 : 11:04:14 PM
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If Yo=-1 and X=0 then Y=A1-1
So Y will not be zero. Is it right?
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malgoska
Poland
36 Posts |
Posted - 07/13/2013 : 05:29:30 AM
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Sorry, my mistake. As exp(0)=1, you should put A1=-y0;
You can also create simpler version of the function with just two parameters in a form y=A*(exp(-x/t1)-1).
Regards |
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Tmlcky
Italy
4 Posts |
Posted - 07/16/2013 : 03:14:15 AM
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It didn' work.
However, I implemented two equations (1 and 2 exp. dec.) I got elsewhere which worked nicely.
Thank you anyway.
Regards
Pasquale Giorio
CNR-ISAFOM
via Patacca, 85
80056- Ercolano (NA),
Italia
tel: +39 081 5746606 (int. 230, 224 or 231)
fax: +39 081 7718045
Email: pasquale.giorio@cnr.it |
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Why this constraint is wrong?