The models for the covering arrays which are used to produce
the initial test suite.

The models are read in by the CASA tool
(http://www.cse.unl.edu/citportal/tools/casa/) and used to
generate covering arrays.

The format of the model files conforms to that required by
CASA tool. Here we only briefly introduce it, and details
can be found at the web site of CASA.

Each model file used here contains exactly three lines:
Line 1: Strength (t)
Line 2: Length (k)
Line 3: Number of events that can be fit into each position (v).
        This line contains k integers, which means the number of
        values for each position. Even if the numbers are the same,
        the k integers still need to be presented.

For example, to generate a 3-way test suite with length-5 test cases
for 4 events which are supposed to appear at any position, the following
model file can be used for the initial test suite:

3
5
4 4 4 4 4