# Successive over-relaxation (SOR) ¶

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The method SOR is introducing a new variable $\omega$ (omega). When omega is 1, then this is the Gauss-Seidel formula. When omega is lesser than one, you should use the Jacobi method. And finally, when omega is greater than one, then you should use this method.

Since we are using this method, we are picking an omega greater than one, which is usually $\omega=1.1$. The SOR formula is

$X^{k+1} = (\frac{1}{\omega} D - L)^{-1} * (b + [((\frac{1}{\omega} - 1) * D + U) * X^{(k)}])$

with

• omega is a number usually
• omega > 0 and < 1: Jacobi
• omega = 1: Gauss-Seidel
• omega > 1: SOR
• PART1: $(\frac{1}{\omega} D - L)^{-1}$
• PART2: $((\frac{1}{\omega} - 1) * D + U)$

## Example using the theory ¶

Using the code we wrote for the Jacobi method,

# ...
##################################
# Complete here: add new variables
##################################
omega <- 1.1
PART1 <- solve(((1/omega) * D) - L)
PART2 <- (1/omega - 1) * D + U

repeat {
# update our vector of values with the formula
Xk <- PART1 %*% (b + PART2 %*% Xk)
# ...
}