This example shows how MSAT can read elasticity matrices from various file formats and from the built-in database. This is often the first task that must be performed by any application built using MSAT. The source code for this example are contained in the file loading_examples.m in the examples/loading directory distributed with MSAT. This directory also contains the data files needed to run the example. Significant parts of the code are reproduced below with explanation.

The "default" data format is a row based text file with two integers and a real number in each row. Column one and two contain the indices (in Voigt notation) of the elastic constant contained in column three (in GPa). Only the constants that are non-zero by symmetry must be provided (and only those in the upper-half of the elasticity matrix). The indices "7 7" stand for density (in kg/m^3). This data format can be read as follows (with or without the density, as needed):

% Load a file in default format assuming file units are GPa
fprintf('Elasticity matrix from "Olivine.txt" - default format:')
C = MS_load('Olivine.txt')
% Load a file in default format assuming file units are GPa and
% density in kg.m^-3
fprintf('Elasticity matrix and density from "Olivine.txt":')
[C,rh] = MS_load('Olivine.txt')

It is also possible to read data from a similar file where the elastic constants are density normalised (and the units of the un-normalised constants must be changed):

% Read density normalised elasticities, where the pre-normalised
% elasticities are in Pa and the density is in kg.m^-3 (i.e. units
% of the elasticity values in the file are m^2.s^-2). Note that
% unit conversion (from Pa to GPa) is performed after
% denormalisation.
fprintf('Elasticity matrix and density from "Olivine.Aij"')
fprintf(' (file data is density normalised):')
[C,rh] = MS_load('Olivine.Aij','Aij','eunit','Pa')

Data stored in the format used by David Mainprice’s EMATRIX program can also be read:

% Load a file in 'ematrix' format
fprintf('Elasticity matrix from "Olivine.Ematrix",')
fprintf(' file format of the ematrix program:')
[C] = MS_load('Olivine.Ematrix','format','ematrix')

MS_load can "expand" the elasticity matrix if the symmetry is provided (Olivine.iso has only two constants, C33 and C66 - the rest of the isotropic matrix is filled in by MSAT).

% File with isotropic data - note symmetry handling.
fprintf('Elasticity matrix and density from "Olivine.iso",')
fprintf(' this is an isotropic aggregate of olivine crystals:')
[C,rh] = MS_load('Olivine.iso','symmetry','iso')

It is often useful to read data from the built-in database of elastic constants:

% Use the built in database.
fprintf('Elasticity matrix and density from the built in database:')
[C,rh] = MS_elasticDB('Olivine')