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FJoel
Germany
5 Posts |
 Posted - 05/24/2018 : 4:40:52 PM
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Origin Ver. and Service Release (Select Help-->About Origin):OriginPro 2017 SR2
Operating System: Win 10
Hi,
Is there a tool for fitting a surface function in a 3D ternary counter plot? In my case I want to fit data points to the Redlich Kister Muggiano function H(x,y,z):
H=x*y*(L0ab+L1ab*(x-y)+L2ab*(x-y)^2)+x*z*(L0ac+L1ac*(x-z)+L2ac*(x-z)^2)+y*z*(L0bc+L1bc*(y-z)+L2bc*(y-z)^2)+x*y*z*(M0*x+M1*y+M2*z);
z=1-x-y;
While L-parameters are known constants and H(x,y,z) is the measured value and M are the wanted parameters.
I used the function builder to define a surface function H(x,y) by combining the two functions. Then performing the fitting procedure, with the open 3D plot. Origin sets for the input values x,y,z as the concentrations. But I want z to be H.
Does anyone knows what I missed to perform the fitting?
Attached you find a picture with the surface I want to fit with the function above.
I hope someone can help me and i really appreciate your support.
Joel
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Edited by - FJoel on 05/24/2018 4:46:34 PM |
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AmandaLu
439 Posts |
Posted - 05/24/2018 : 10:53:58 PM
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Hi,
On the Data Selection of Nonlinear Curve Fit dialog, you can specify which column to be independent variable and which to be dependent variable.
I cannot fully understand your problem. If the user defined function only has two independent variables H(x,y), how did Origin “set for the input values x,y,z as the concentrations”? Can you tell me the function you defined and how Origin set the input data?
Thanks,
Amanda
OriginLab Technical Service
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FJoel
Germany
5 Posts |
Posted - 05/25/2018 : 03:57:53 AM
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Hi Amenda,
Thank you for your replay.
With the condidtion that x+y+z=1 in the ternary I reduced the H(x,y,z) function to:
H=x*y*(L0ab+L1ab*(x-y)+L2ab*(x-y)^2)+x*(1-x-y)*(L0ac+L1ac*(x-(1-x-y))+L2ac*(x-(1-x-y))^2)+y*(1-x-y)*(L0bc+L1bc*(y-(1-x-y))+L2bc*(y-(1-x-y))^2)+x*y*(1-x-y)*(M0*x+M1*y+M2*(1-x-y));
/*
0<x<1;
0<y<1;
/*
with x,y as independent variables, H as dependend variable, and L as constants.
I added a screenshot of the data selection window.
Do the fit from the workbook,the H varibale can be choosed as z but Origin collaps right after starting the fit.
Hope the question gots more clear and I am very thankfull for your help!
Joel
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AmandaLu
439 Posts |
Posted - 05/25/2018 : 04:53:04 AM
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Hi,
If your 3D ternary was created from column XYZZ, the dependent variable in your fitting should be the second Z column. But in the screenshot you show, you chose the first Z to fit?
You can send your data and user defined function (FDF file) to tech@originlab.com so we can check.
Thanks,
Amanda
OriginLab Technical Service
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Surface fit in 3D ternary plot with Redlich-Kister