Runge-Kutta 2

*To*: mathgroup at smc.vnet.net*Subject*: [mg132547] Runge-Kutta 2*From*: amzoti <amzoti at gmail.com>*Date*: Thu, 10 Apr 2014 03:09:17 -0400 (EDT)*Delivered-to*: l-mathgroup@mail-archive0.wolfram.com*Delivered-to*: l-mathgroup@wolfram.com*Delivered-to*: mathgroup-outx@smc.vnet.net*Delivered-to*: mathgroup-newsendx@smc.vnet.net

After spending some time using the Mathematica documentation I implemented the Runge-Kutta-2 routines below. I am hoping someone can validate what I did and tell me that it is correct (especially the Butcher Tableau I used) and the step size h=0.1. ClassicalRungeKuttaCoefficients[4, prec_] := With[{amat = {{1/2}}, bvec = {0, 1}, cvec = {1/2}}, N[{amat, bvec, cvec}, prec]] {xf, yf} = {x, y} /. First@NDSolve[{x'[t] == -y[t], y'[t] == x[t], x[0] == 1, y[0] == 0}, {x, y}, {t, 0, 6}, Method -> {"ExplicitRungeKutta", "DifferenceOrder" -> 4, "Coefficients" -> ClassicalRungeKuttaCoefficients}, StartingStepSize -> 1/10]; xl = MapThread[Append, {xf["Grid"], xf["ValuesOnGrid"]}] yl = MapThread[Append, {yf["Grid"], yf["ValuesOnGrid"]}] We can find a closed form solution to this problem as: s = DSolve[{x'[t] == -y[t], y'[t] == x[t], x[0] == 1, y[0] == 0}, {x, y}, t] Is there an automated way to update and step through each variant of RK-2, RK-3, RK-4, ... without having to manually enter the Butcher values (in other words, I want to step through each variant of RK-n and compare the errors (a table of that would be great))? There is a hint of this at: http://reference.wolfram.com/mathematica/tutorial/NDSolveExplicitRungeKutta.html Lastly, is there a better approach?