The file should contain a matrix in the format such as
2 4\break 1 1 1 1\break 1 2 3 4\break
The first two numbers are the numbers of rows and columns.
The object getMatrix is a method function.
The source of this document is in /build/reproducible-path/macaulay2-1.25.05+ds/M2/Macaulay2/packages/FourTiTwo.m2:291:0.