An Improved Four-Step Method

6 An Improved Four-Step Method. - Simos and Williams103 have introduced the following four-step method (with one free parameter), based on the method developed by Henrici3 and Simos and Williams 102 

The method is of algebraic order 6. It has been proved that for a = 3355 the phase-lag is of order 8. The interval of periodicity is equal to 0,6(231 9 - - = (0. 7.26).This method is rather more complicated in its matrix form. The eigenvalue equation now takes the form 

By introducing the variable w = h2Ey, the above equation can be transformed into the standard eigenvalue problem 

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