Mismatch Between Impedance Matrix and Current Eigenvector

Hello, I've recently started using Feko and I have been trying to export the impedance matrix as well as the current eigenvector for further analysis. The current eigenvector that I extract from the .str output file has a number of elements corresponding to the total number of basis functions produced by Feko. The impedance matrix, however, has elements corresponding to the number of unknown basis functions rather than all of the basis functions. Why are some basis functions already known and what could I do to reconcile the difference in dimensions between the current eigenvector and the impedance matrix? In other words how do I make it so the vector is Nx1 and the matrix is NxN.

On a side note, I assume that the two elements in each row of the .str file correspond to the real part and the imaginary part of the current, respectively, correct?

Cheers