Higher order modes computation in RF cavities

Two methods are used to compute higher order modes of RF cavities. One combines point successive overrelaxation, Rayleigh quotient, and orthogonalization against lower order modes. The other utilizes Rayleigh quotient iteration and biconjugate gradient. Both methods have been implemented in the authors´ program, since the former is preferred for computing the lowest n modes while the latter is suitable for picking up a single higher mode. They can also be combined to produce comprehensive strategies more powerful than either one can provide alone