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@@ -13,6 +13,60 @@ You might then want to consider using a tool such as ImageMagick to then convert For the cliché set you'll want to keep the exponent at 2. For more info on the exponent, read through [Wikipedia's fine article](http://wikipedia.org/wiki/Mandelbrot_set). +### Options in detail + +The `-s` and `-i` are the only two mandatory arguments. All others will assume +their default values (shown here in brackets) if left unspecified. + +Also note that `-N` should always be used together with `-T`. + + -s size - Integer. Height and width of image in pixels + -s max_iterations - Integer. Maximum number of iterations to use to + determine if number is in the fractal set. + -e exponent - Float. Exponent to use in the fractal's calculation. (2) + -c cores - Integer > 0. Number of cores to assume computer has. + (sysconf(_SC_NPROCESSORS_ONLN)) + -t thread_multiplier - Integer > 0. Coefficiant to multiply cores by in + order to achieve count of worker threads to use. (1) + -N cluster_id - 0 <= Integer < cluster_total. A unique ID used to determine + which sections of the image this instance should work on. + Clustering explained in the 'Clustering' section of this + document. (0) + -T cluster_total - 0 < Integer <= size. Total count of worker instances in + this cluster. + +## Clustering + +This program allows workload for an image to be spread across multiple +instances of the program. This means, for example, that you can parallel the +computation on an image between multiple computers. + +### Example + +Let's say we're generating a quick mandelbrot 20000 pixels in width and with +100 iterations max. We want to spread the load between two identical computers +in order to perhaps halve the computation time: + + # On computer #1: + ./mandelbrot -s 20000 -i 100 -T 2 -N 0 > 0.pgm + # On computer #2: + ./mandelbrot -s 20000 -i 100 -T 2 -N 1 > 1.pgm + +At the heart of it, each instance will only calculate half of the image. This +is achieved by (in this case) getting the instance with ID 0 to work on +the 1st, 3rd, 5th, and other odd numbered columns, while the instance with ID 1 +will work on the columns in between. To perhaps point out the obvious(?), +interlacing is used in a bid to spread the workload more evenly across cluster +members. + +This will result in two separate pgm files, each 10000x20000 pixels. +They must be vertically interlaced in order to form the whole desired image. +This extends to any number of cluster members less than or equal to the image +size, since the interlacing can only split by column, not row. + +I currently have a tool that I use to interlace the resultant images. I'm +working on polishing it so it is publish-worthy. + ## Notes 1. By default, this has your CPU over a barrel. |