Henrik Brandén Sverker Holmgren Per Sundqvist Discrete Fundamental Solution Preconditioning for Hyperbolic Systems of PDE. 35-60 2007 30 J. Sci. Comput. 1 http://dx.doi.org/10.1007/s10915-005-9018-z db/journals/jscic/jscic30.html#BrandenHS07