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CMcRitchie
United Kingdom
3 Posts |
 Posted - 07/28/2016 : 08:37:47 AM
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Hi,
I wondered if it was possible to use the Fitting Function Organiser in the following way:
Using x,y data where 0<x<2000
Create a function that applies two or more equations to the experimental data over different ranges of x
e.g. Equation 1: y = a + (b*x) where 0<x<40
Equation 2: y = a + (b*x) where 40<x<2000
I know I can manually select different parts of the experimental data and apply each function in turn, however it would be really beneficial for me if this could be done using a user created function.
Any help would be much appreciated,
Thanks |
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Hideo Fujii
USA
1582 Posts |
Posted - 07/28/2016 : 09:50:20 AM
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Hi CMcRitchie,
I think you can consider the built-in functions in the Piecewise category such as PWL2 for two segments
(or PWL3 for three segments):
http://www.originlab.com/doc/Origin-Help/PWL2
Please take a look.
--Hideo Fujii
OriginLab |
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CMcRitchie
United Kingdom
3 Posts |
Posted - 07/28/2016 : 10:06:52 AM
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quote:
Originally posted by Hideo Fujii
Hi CMcRitchie,
I think you can consider the built-in functions in the Piecewise category such as PWL2 for two segments
(or PWL3 for three segments):
http://www.originlab.com/doc/Origin-Help/PWL2
Please take a look.
--Hideo Fujii
OriginLab
Hi Hideo Fujii,
Thanks for your suggestion. Do you know if there is a similar alternative that would accommodate non-linear functions?
Thanks,
CMcRitchie |
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Hideo Fujii
USA
1582 Posts |
Posted - 07/28/2016 : 10:48:58 AM
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Hi CMcRitchie,
> Do you know if there is a similar alternative that would accommodate non-linear functions?
Currently, there is no built-in piecewise non-linear functions. So, you need to make a user-defined function
generally in the following way: y0=function1(x0);
if( x<x0 ) y=function1(x);
else y=function2(x); //function2 is a curve which passes (x0,y0) to connect to function1
The hard (if not impossible) part may be to find the form of function2 by solving y0=function2(x0) analytically.
Good luck.
--Hideo Fujii
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CMcRitchie
United Kingdom
3 Posts |
Posted - 07/28/2016 : 10:59:02 AM
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quote:
Originally posted by Hideo Fujii
Hi CMcRitchie,
> Do you know if there is a similar alternative that would accommodate non-linear functions?
Currently, there is no built-in piecewise non-linear functions. So, you need to make a user-defined function
generally in the following way: y0=function1(x0);
if( x<x0 ) y=function1(x);
else y=function2(x); //function2 is a curve which passes (x0,y0) to connect to function1
The hard (if not impossible) part may be to find the form of function2 by solving y0=function2(x0) analytically.
Good luck.
--Hideo Fujii
Again thanks for your help. I have started to play around with using 2 equations, if I were to introduce a third equation, what do I write as the code to introduce an additional condition on the range of x? i.e. go from PWL2 to PWL3
e.g.
if (x<x0) y=function1(x);
if (x0<=x<=xa) y=function2(x);
else y=function3(x);
what is the correct command for the 2nd line? I assume repeating "if" is not correct.
Many thanks,
CMcRitchie |
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Hideo Fujii
USA
1582 Posts |
Posted - 07/28/2016 : 11:15:45 AM
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Hi CMcRitchie,
> if (x<x0) y=function1(x);
> if (x0<=x<=xa) y=function2(x);
> else y=function3(x);
> what is the correct command for the 2nd line?
> I assume repeating "if" is not correct.
The syntax should be like (assuming function type is Origin C):if(x<x0) y=function1(x); //x<x0
else if(x<xa) y=function2(x); //x0<=x<xa
else y=function3(x); //xa<=x Hope this helps.
--Hideo Fujii
OriginLab
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Topic |
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Fitting 2 equations to different ranges of x