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NL fit with user defined eqn did not converge

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[quote][i]Originally posted by rainbowkoala[/i]
[br]Origin Ver. and Service Release (Select Help-->About Origin): OriginPro 8.5.0 SR1 
Operating System: win7

I typed the following eqn to use as user defined and find the 3 unknown parameters,(a,b,c)
y =(1/2)*a*sin(b*3.14/2)/(cosh(b*(ln(x*c)))+cos(b*3.14/2))
It compiles, but my function do not converge.
Then I draw a specified plot using following the parameters:
a=2, b=0.8, c=0.08. That is 
y=(1/2)*2*sin(0.8*3.14/2)/(cosh(0.8*(ln(Col(B1)*0.08)))+cos(0.8*3.14/2)).
I did  NLfitting use the defined eqn. Parameters a,b,c are properly initialized (a=2, b=0.8, c=0.08.). I specified bounds on the parameters: 1<a<3, 0<b<1, 0.07<b<0.08.
My function do not converge at all.

Please find more details in the insert image.
The original data is in the attachment.
Thanks for your help.

[img]http://www.originlab.com/ftp/forum_and_kbase/Images/user defined function PROBLEM.gif[/img]

[url]http://www.originlab.com/ftp/forum_and_kbase/Images/user defined function.ogw[/url]
[/quote]

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T O P I C R E V I E W
rainbowkoala	Posted - 09/28/2013 : 08:34:52 AM Origin Ver. and Service Release (Select Help-->About Origin): OriginPro 8.5.0 SR1 Operating System: win7 I typed the following eqn to use as user defined and find the 3 unknown parameters,(a,b,c) y =(1/2)asin(b3.14/2)/(cosh(b(ln(xc)))+cos(b3.14/2)) It compiles, but my function do not converge. Then I draw a specified plot using following the parameters: a=2, b=0.8, c=0.08. That is y=(1/2)2sin(0.83.14/2)/(cosh(0.8(ln(Col(B1)0.08)))+cos(0.83.14/2)). I did NLfitting use the defined eqn. Parameters a,b,c are properly initialized (a=2, b=0.8, c=0.08.). I specified bounds on the parameters: 1<a<3, 0<b<1, 0.07<b<0.08. My function do not converge at all. Please find more details in the insert image. The original data is in the attachment. Thanks for your help. http://www.originlab.com/ftp/forum_and_kbase/Images/user defined function.ogw
2 L A T E S T R E P L I E S (Newest First)
rainbowkoala	Posted - 10/05/2013 : 03:36:47 AM Hi Shirley, Thank you for the response. The data has been sent to tech@originlab.com. Please find more details in the email. quote: Originally posted by Shirley_GZ Hi, Sorry, I failed to download your data, please send the data to tech@originlab.com and quote this post. Thanks, Shirley Originlab Technical Service Team
Shirley_GZ	Posted - 09/30/2013 : 06:33:27 AM Hi, Sorry, I failed to download your data, please send the data to tech@originlab.com and quote this post. Thanks, Shirley Originlab Technical Service Team

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