Does R optimise the order of matrix multiplications? -

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if multiplying 3 matrices together, abc. depending on size of matrices may more efficient perform either (ab)c or a(bc). if evaluate:

a %*% b %*% c

will optimised in anyway?

thanks colonel beauvel setting me on right path - test it. using example wikipedia , scaling suitably:

> mult <- 100 > ar <- 10 * mult > ac <- 30 * mult > br <- 30 * mult > bc <- 5 * mult > cr <- 5 * mult > cc <- 60 * mult >  > <- matrix(rnorm(ar * ac), ar, ac) > b <- matrix(rnorm(br * bc), br, bc) > c <- matrix(rnorm(cr * cc), cr, cc) >  > system.time({ (a %*% b) %*% c })     user  system elapsed      3.01    0.00    3.01  > system.time({ %*% (b %*% c) })     user  system elapsed      25.34    0.03   25.37  > system.time({ %*% b %*% c })     user  system elapsed      2.98    0.00    2.98  > system.time({ t(c) %*% t(b) %*% t(a) })    user  system elapsed    25.61    0.03   25.64

incidently - r evaluates left right.


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