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Faddeeva Package: complex error functions

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26 Oct 2012 (Updated )

C++ MEX plugins to compute error functions (erf, erfc, erfi, erfcx, Faddeeva, ...) of complex args

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Description

C++ source code for compiled plugins (MEX files) to compute various error functions for complex arguments:

** Faddeeva_erf(z) -- the error function
** Faddeeva_erfc(z) = 1 - erf(z) -- complementary error function
** Faddeeva_erfi(z) = -i erf(iz) -- imaginary error function
** Faddeeva_erfcx(z) = exp(z^2) erfc(z) -- scaled complementary error function
** Faddeeva_w(z) = exp(-z^2) erfc(-iz) -- Faddeeva function
** Faddeeva_Dawson(z) = 0.5 sqrt(pi) exp(-z^2) erfi(z) -- Dawson function

From e.g. the Faddeeva function, one can also obtain the Voigt functions and other related functions.

Assuming you have a C++ compiler (and have configured it in MATLAB with mex -setup), compile by running the included Faddeeva_build.m script in MATLAB:

  Faddeeva_build

All of the functions have usage of the form:
  w = Faddeeva_w(z)
or optionally Faddeeva_w(z, relerr), where relerr is a desired relative error (default: machine precision). z may be an array or matrix of complex or real numbers.

This code may also be downloaded from

  http://ab-initio.mit.edu/Faddeeva

along with documentation and other versions. As described in the source code, this implementation uses a combination of algorithms for the Faddeeva function: a continued-fraction expansion for large |z| [similar to G. P. M. Poppe and C. M. J. Wijers, "More efficient computation of the complex error function," ACM Trans. Math. Soft. 16 (1), pp. 38–46 (1990)], and a completely different algorithm for smaller |z| [Mofreh R. Zaghloul and Ahmed N. Ali, "Algorithm 916: Computing the Faddeyeva and Voigt Functions," ACM Trans. Math. Soft. 38 (2), 15 (2011).]. Given the Faddeeva function, we can then compute the other error functions, although we must switch to Taylor expansions and use other tricks in certain regions of the complex plane to avoid cancellation errors or other floating-point problems.

MATLAB release MATLAB 7.14 (R2012a)
Other requirements C++ compiler.
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Comments and Ratings (5)
28 Feb 2014 Ian

One update I would really like to see in this package is the derivative functions, at least for W(z). As pointed out in Zaghloul and Ali, the derivative functions of W(z) (equations 21-23) become numerically unstable near dV/dx = 0 (V=real(W(z)), at the peak of the Voigt function. This can cause problems when trying to compute analytical Jacobians for doing nonlinear fits of the Voigt function to optical spectra.

Since you are already using the Zaghloul and Ali algorithm in this region, it would be helpful to also use their method to output a function, say Faddeeva_dw(z) = dV/dx + i*dL/dx (L=imag(W(z)). The corresponding y derivatives can then be trivially computed.

27 Feb 2014 Ian

Works as advertised and is extremely fast.

12 Feb 2013 Niklas  
15 Dec 2012 Steven G. Johnson

It won't work with lcc, since that is a C compiler, not a C++ compiler. The failure to compile with Visual C++ is a bug, which is fixed in the latest release on my web site (and which should appear on Matlab Central shortly).

11 Dec 2012 alan

Hello, Love this program. I have it up and running on my mac to simulate voigt broadening. Im trying to add this functionality to a lab computer running win32 matlab 7.12.0 (R2011a), but I cannot successfully compile with mex.

With Lcc-win32 C 2.4.1 in C:\PROGRA~1\MATLAB\R2011a\sys\lcc: lcc preprocessor error: .\Faddeeva.hh:30 .\Faddeeva_mex.cc:35 Faddeeva_w_mex.cc:3 Could not find include file complex

full verbose: http://pastebin.com/YyLYYe8C

With Microsoft Visual C++ 2010 Express in C:\Program Files\Microsoft Visual Studio 10.0: Faddeeva.cc Faddeeva.cc(184) : error C2124: divide or mod by zero Faddeeva.cc(822) : error C3861: 'copysign': identifier not found C:\PROGRA~1\MATLAB\R2011A\BIN\MEX.PL: Error: Compile of 'Faddeeva.cc' failed.

full verbose: http://pastebin.com/K4LPd9FN

The only instances of complex.h are in a pythonwx folder not related to matlab. I see that it was released for R2012a. Does the package need a specific C++ compiler?

Updates
29 Oct 2012

Improve accuracy in Re[w(z)] taken by itself.

30 Oct 2012

note how to compute erfi using Faddeeva function

05 Nov 2012

Now includes separate plugins for all of the error functions.

17 Dec 2012

portability fixes, slight accuracy improvements

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