private double[][][] dominage = new double[ 4 ][][];

That being an array of an array of an array of doubles.
With the new operator, you fix the first dimension on 4 in this case.

When using, you will do things like:
dominage[ 0 ] = new double[ 5 ][];
dominage[ 0 ][ 0 ] = new double[ 6 ];
dominage[ 0 ][ 0 ][ 0 ] = Math.PI;

etc.

If you want a fixed 3D matrix, then you would declare as:

private double[ , , ] dom = new double[ 4, 5, 6 ];

This is obviously a 4x5x6 matrix.

Or any combination of the above.
Have fun. :)

David

Note: I used "dominage" as name, instead of "m_dominage". The first is
C# convention (camel case for private data members), the latter C++
convention.