About Using the MATLAB built-in function in fitting process

2015 12 20
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更新时间：2015 12 21
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Hello, I'm using custom equations in fitting my data. The problem is that these equations contain one or more MATLAB built-in functions (e.g., expint, lambertw,..) and it takes so long (about 20 minutes) to converge. Is there any way so that I can decrease the accuracy of these built-in functions so that the convergence become faster? Or any idea to accelerate the fitting process?
Thanks.

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回答（1 个）

Walter Roberson
Walter Roberson 2015-12-20

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expint() is available both numerically and in the Symbolic Toolbox. lambertw is available only in the symbolic toolbox, but a numeric version of it is available in the File Exchange
If you need to use the symbolic toolbox then you can decrease computation time by setting Digits to lower.

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Amr Sadek
Amr Sadek 2015-12-20
Thank you for your answer. I use these equations in a GUI. So I'm using the MATLAB (numeric version) not the Symbolic Toolbox.
Walter Roberson
Walter Roberson 2015-12-21
How were you calling a numeric lambertw ? Were you already using the version from the File Exchange?
Amr Sadek
Amr Sadek 2015-12-21
I'm using MATLAB 2014a. The Lambertw function is a built-in function. I don't use any File Exchange.
Walter Roberson
Walter Roberson 2015-12-21
Please use
which -all lambertw
to see which LambertW implementation you are getting. The two that are documented are Symbolic Toolbox, MATLAB Interface and Symbolic Toolbox, MuPAD Engine
There are a few different implementations in the File Exchange, including the one by Cleve, linked above, and another by D.A. Barry at http://www.mathworks.com/matlabcentral/fileexchange/3644-real-values-of-the-lambert-w-function
Amr Sadek
Amr Sadek 2015-12-21
I'm actually using lambertw(x) for the first (principal) branch and lambertw(-1,x) for the second branch in my codes. Is that what you mean?
Amr Sadek
Amr Sadek 2015-12-21
which -all lambertw
D:\...\MATLAB 2014a\toolbox\symbolic\symbolic\@single\lambertw.m % single method
D:\...\MATLAB 2014a\toolbox\symbolic\symbolic\@double\lambertw.m % double method
D:\...\MATLAB 2014a\toolbox\symbolic\symbolic\@sym\lambertw.m % sym method

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Amr Sadek
Amr Sadek
2015-12-20

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Amr Sadek
2015-12-21

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