From: Nathan S. Watson-Haigh <nathan.watson-haigh_at_csiro.au>

Date: Thu, 26 Mar 2009 11:48:41 +1000

I want to split work into a number of unequal chunks such that the sum of the values in each chunk is approximately equal.

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https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code. Received on Thu 26 Mar 2009 - 00:53:44 GMT

Date: Thu, 26 Mar 2009 11:48:41 +1000

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I have some data generated as follows:

<code>

n <- 2000

work <- vector()

for(x in 1:n) {

work[x] <- sum(1:(n-x+1))

}

plot(work)

</code>

- -----------------

I want to split work into a number of unequal chunks such that the sum of the values in each chunk is approximately equal.

The numbers in "work" are proportional to the amount of work to be performed for each value of x by a function I've written. i.e. For each value of x, there are work[x] * y calculations to be performed (where y is a constant).

I've written a parallel version of my function where I simply assign z number of x values to each slave. This is not ideal, since a slave that gets the 1:z smallest values of x will take longer to compute than the (n-z+1):n set of x values. For example, if I have 4 slaves available:

slave 1 processes x in 1:500

slave 2 processes x in 501:1000

slave 3 processes x in 1001:1500

slave 4 processes x in 1501:2000

This means the total work performed by each slave is:

slave 1 sum(work[1:500]) = 771708500 slave 2 sum(work[501:1000]) = 396458500 slave 3 sum(work[1001:1500]) = 146208500 slave 4 sum(work[1501:2000]) = 20958500

Manually plitting work into chunks where the sum of the values for the chunks is approximately equal, I get the following:

sum(work[1:184])

[1] 335533384

> sum(work[185:415])

[1] 334897871

> sum(work[416:745])

[1] 334672085

> sum(work[746:2000])

[1] 330230660

I need to be able to do this automatically for any value of n and I think I should be able to do this by calculating the area under the curve and slicing it into equally sized regions, but don't really know how to get there from what I've said above!

Cheers,

Nathan

- --
- -------------------------------------------------------- Dr. Nathan S. Watson-Haigh OCE Post Doctoral Fellow CSIRO Livestock Industries Queensland Bioscience Precinct St Lucia, QLD 4067 Australia

Tel: +61 (0)7 3214 2922 Fax: +61 (0)7 3214 2900 Web: http://www.csiro.au/people/Nathan.Watson-Haigh.html - --------------------------------------------------------

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https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code. Received on Thu 26 Mar 2009 - 00:53:44 GMT

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