MAG-MIX© download


Preamble
Rocks and sediments inevitably contain mixtures of magnetic minerals, grain sizes, and weathering states. Most rock magnetic interpretation techniques rely on a set of value parameters, such as susceptibility and isothermal/anhysteretic remanent magnetisation (ARM or IRM). These parameters are usually interpreted in terms of mineralogy and domain state of the magnetic particles. In some cases, such interpretation of natural samples may be misleading or inconclusive.

A less constrained approach to magnetic mineralogy models is based on the analysis of magnetisation curves, which are decomposed into a set of elementary contributions. Each contribution is called a magnetic component, and characterises a specific set of magnetic grains with a unimodal distribution of physical and chemical properties. Magnetic components are related to specific biogeochemical signatures rather than representing traditional categories, such as single domain magnetite. This unconventional approach can be regarded as a kind of principal component analysis (PCA) that gives a direct link to the interpretation of natural processes on a multidisciplinary level. Since magnetic components rarely occur alone in natural samples, unmixing techniques and rock magnetic models are interdependent.
Valuable information for rock magnetic and environmental studies can be obtained directly from the coercivity distribution of the sample, which provides a richness of details hidden in the measurement curve.

What is MAG-MIX?
The software package MAG-MIX provides computer programmes for the analysis of isothermal magnetisation curves* and coercivity distributions and was developed by Ramon Egli. This first release includes the programmes CODICA and GECA. It consists of two packages: CODICA (COercivity DIstribution CAlculator) and  GECA (GEneralised Coercivity Analyser).

*The term magnetisation curve has here and in the following the meaning of an acquisition curve, alternating field demagnetisation curve or backfield curve (latter also called direct current demagnetisation).


What does CODICA do?
CODICA is a programme that calculates the coercivity distribution of a magnetisation curve and estimates the measurement errors. CODICA eliminates efficiently measurement noise from acquisition or demagnetisation curves of remanent magnetisation (based on rescaling procedures) and calculates then the derivative (also called coercivity distribution or coercivity spectrum).



What does Geca do?
GECA is a programme for modelling a coercivity distribution as a linear combination of special model functions, that are supposed to represent the coercivity distribution of specific groups of magnetic particles, called components (= unmixing). A Pearson's X 2 goodness of fit test evaluates the number of functions required for the best-fit and an error estimation allows to calculate the confidence limit for each model parameter.


Requirements
Both programmes are written in Mathematica, a programming language similar to other traditional computer languages such as C, Pascal or FORTRAN. The usage of CODICA implies that Mathematica is installed on your computer. MAG-MIX has been developed for Mathematica 5.0 under Windows, but with small code modifications it is also compatible with Mathematica for Linux/Unix.  At least 128 MB RAM and a 1 GHz CPU are recommended.


Installation
1. Install Mathematica on your computer.
2. Download the zip-file from below, store it in a local directory and unpack it.
3. Install CODICA. To install CODICA 5.0 copy the source code file MAG_MIX_1/CODICA/Install/Codica.m into the following directory:
    C:/.../WolframResearch/Mathematica/5.0/AddOns/StandardPackages/Utilities
    whereby C:/.../ depends on the installation of Mathematica on your computer.

4. To install GECA, copy the source code file MAG_MIX_1/GECA/Install/Geca.m and the file MAG_MIX_1/GECA/Install/components.txt into the
    following directory:
   C:/.../Wolfram Research/Mathematica/5.0/AddOns/StandardPackages/Utilities
   whereby C:/.../ depends on the installation of Mathematica on your computer.


Download
Both releases can be downloaded following the links below.

MAG-MIX Release 1 (2005), Mathematica v.5.0 for Windows must be installed in your computer.
The zip file contains: installation instructions for CODICA 5.0 and GECA 2.1, the source code (files Codica.m, Geca.m), the reference manual (pdf-format) and examples (including data).

MAG-MIX_r1.zip (4.6 Mb)
Manual only
Here you can download the reference manual, including theoretical aspects.

Manual MAG-MIX 5.0 (2005) (4.1 Mb)

Notice
Your feedback is important to improve the MAG-MIX. If you encounter problems in using the programmes, or if you have suggestions, please do not hesitate to contact the author by e-mail: eglix007@umn.edu.


References
Egli, R., Analysis of the field dependence of remanent  magnetization  curves, Journal  of Geophysical   Research,   108   (B2),   2081,   doi 10.1029/2002JB002023, 2003.

Egli, R.,  Characterization of individual rock magnetic components by analysis of remanence curves, 2. fundamental properties of coercivity distributions, Physics and Chemistry of the Earth, 29, 851-867, 2004.

Heslop, D.,  Dekkers, M.J., Kruiver, P.P. and  I. H. M. van Oorschot, Analysis of isothermal remanent magnetization acquisition curves using the expectation-maximization algorithm, Geophysical Journal International,148, 58-64, 2002.

Kruiver P.P.,  Dekkers M.J. and D. Heslop, Quantification of magnetic coercivity components by the analysis of acquisition curves of isothermal remanent magnetisation, Earth and Planetary Science Letters, 189, 269-276, 2001.

Spassov, S., Egli, R., Heller, F., Nourgaliev, D.K. and J. Hannam, Magnetic quantification of urban pollution sources in atmospheric particulate matter, Geophysical Journal International, 159, 555-564, 2004.