Stacking of DOFs in Abaqus

I am studying the response of a bridge in MATLAB, and have successfully retrieved mass and stiffness matrices from Abaqus using the following keywords:

*Step

*Matrix generate, STIFFNESS, MASS

*Matrix output, STIFFNESS, MASS, FORMAT=COORDINATE

*End step 

This gives matrices on a mathematical form, very well suited for use with MATLAB. 

Further I want to add additional mass and stiffness to parts of the structure in MATLAB, and thus need to know which degrees of freedom the different elements in the matrices correspond to. Does anyone know how Abaqus stack the degrees of freedom in these matrices (or simpler perhaps: the displacement vector in the equation of motion)? I know the node numbers, but need the position of the degrees of freedom in the vector or/and matrix.

Every reply is much appreciated! 

Sincerely,

Knut Andreas Kvåle