Fastest way to do this double summation?

Question

What is the fastest way to do this summation in R? This is what I have so far ``` ans = 0 for (i in 1:dimx[1]){ for (j in 1:dimx[2]){ ans = ans + ((x[i,j] - parameters$mu)^2)/(parameters$omega_2[i]*parameters$sigma_2[j]) } } ``` where `omega_2`, and `sigma_2` are omega^2 and sigma^2 respectively.

Accepted Answer

Nothing fancy:

```
# sample data
m <- matrix(1:20, 4)
sigma <- 1:ncol(m)
omega <- 1:nrow(m)
mu <- 2

sum(((m - mu) / outer(omega, sigma))^2)
```

Fastest way to do this double summation?

Solution

Problem