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hacchaaban
Denmark
2 Posts |
 Posted - 07/31/2019 : 10:21:56 AM
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I have the x and y data and I am trying to fit it to the following function: y = exp(-g/R*x)/(1+exp(-g/R*x), r is the gas constant (8.3145 J/(mol*K)), and g(Gibbs energy- the value that I want to find)is the only unknown parameter
When creating the function I added x as the independent variable, y as the dependent variable, and R as a constant, and g as the parameter. The data follow an S-form but when I fit the data I get a line for the fit in the bottom om the figure, and not fitted to the data.
Here are my x and y values:
x data:
293,15
294,15
295,15
296,15
297,15
298,15
299,15
300,15
301,15
302,15
303,15
304,15
305,15
306,15
307,15
308,15
309,15
310,15
311,15
312,15
313,15
314,15
315,15
316,15
317,15
318,15
319,15
320,15
321,15
322,15
323,15
324,15
325,15
326,15
327,15
328,15
329,15
330,15
331,15
332,15
333,15
334,15
335,15
336,15
337,15
338,15
339,15
340,15
341,15
342,15
343,15
344,15
345,15
346,15
347,15
348,15
349,15
350,15
351,15
352,15
353,15
354,15
355,15
356,15
357,15
358,15
359,15
360,15
361,15
y values:
1
0,97576
0,98303
0,9886
0,96893
0,971
0,94832
0,9269
0,93655
0,92935
0,91037
0,8979
0,88926
0,8949
0,87848
0,88155
0,88832
0,8721
0,84917
0,85462
0,8394
0,84153
0,81572
0,8052
0,79574
0,7866
0,75916
0,74381
0,71381
0,69659
0,66226
0,61741
0,57457
0,51807
0,45662
0,42624
0,36091
0,33511
0,31287
0,27817
0,27992
0,25211
0,24817
0,22192
0,21553
0,22155
0,21121
0,18497
0,18108
0,16204
0,13555
0,10573
0,0788
0,0761
0,06827
0,06402
0,06007
0,06552
0,0513
0,03245
0,04316
0,02831
0,01766
0,02073
0,02242
0,00783
0,00583
-0,00238
-0,0052
Hope you can help
Br
Hussein
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YimingChen
1685 Posts |
Posted - 07/31/2019 : 10:58:41 AM
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Hi,
It could be that you are missing an offset for x. I replaced x with x-xc, the fitting is more reasonable. see below
James |
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hacchaaban
Denmark
2 Posts |
Posted - 07/31/2019 : 12:52:01 PM
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Hi James,
thanks a lot.
Could you send me the FDF file, or tell me how to add the offset to x, as I get the same when I add xc as a parameter?
My email is hacchaaban@gmail.com
I am new to origin. Thanks!
Hussein
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Edited by - hacchaaban on 07/31/2019 1:16:12 PM |
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YimingChen
1685 Posts |
Posted - 07/31/2019 : 2:13:14 PM
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Hi,
I sent you the fdf file. By the way, you need to set the initial value of the fitting parameters as below.
James |
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Nonlinear curve fitting