Heun's method

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In mathematics and computational science, Heun's method, named after Karl L. W. M. Heun, is a numerical procedure for solving ordinary differential equations (ODEs) with a given initial value. It can be seen as an extension of the Euler method into a two-stage second-order Runge-Kutta method.

The procedure for calculating the numerical solution to the initial value problem

y'(t) = f(t,y(t)), \qquad \qquad y(t_0)=y_0,

by way of Heun's method, is to first calculate the intermediate value \tilde{y}_{i+1} and then the final approximation yi + 1 at the next integration point.

\tilde{y}_{i+1} = y_i + h f(t_i,y_i)
y_{i+1} = y_i + \frac{h}{2}(f(t_i, y_i) + f(t_{i+1},\tilde{y}_{i+1})).

[edit] Derivation

The scheme can be compared with the implicit trapezoidal method, but with f(ti + 1,yi + 1) replaced by f(t_{i+1},\tilde{y}_{i+1}) in order to make it explicit. \tilde{y}_{i+1} is the result of one step of Euler's method on the same initial value problem.

So, the Heun's method is a predictor-corrector method with forward Euler's method as predictor and trapezoidal method as corrector.

[edit] Runge-Kutta method

Heun's method is a two-stage Runge-Kutta method, and can be written using the tableau

0
1 1
1/2 1/2
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