Abstract: Systems and methods are provided for approximating an electric current on a surface of an object. A mesh is received. A matrix comprising a system of equations is generated based on the mesh. An entry of the matrix is associated with (i) a source function that approximates an electric current on the surface of the object, and (ii) a test function that tests a field of the source function on the surface. A near part of the matrix and a far part of the matrix are determined. The far part of the matrix is represented using a submatrix that is based on Gaussian points on elements of the mesh. The electric current on the surface of the mesh is calculated by solving the system of equations of the matrix.