package coordinate
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// Config is used to set the parameters of the Vivaldi-based coordinate mapping
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// algorithm.
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//
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// The following references are called out at various points in the documentation
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// here:
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//
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// [1] Dabek, Frank, et al. "Vivaldi: A decentralized network coordinate system."
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// ACM SIGCOMM Computer Communication Review. Vol. 34. No. 4. ACM, 2004.
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// [2] Ledlie, Jonathan, Paul Gardner, and Margo I. Seltzer. "Network Coordinates
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// in the Wild." NSDI. Vol. 7. 2007.
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// [3] Lee, Sanghwan, et al. "On suitability of Euclidean embedding for
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// host-based network coordinate systems." Networking, IEEE/ACM Transactions
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// on 18.1 (2010): 27-40.
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type Config struct {
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// The dimensionality of the coordinate system. As discussed in [2], more
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// dimensions improves the accuracy of the estimates up to a point. Per [2]
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// we chose 8 dimensions plus a non-Euclidean height.
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Dimensionality uint
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// VivaldiErrorMax is the default error value when a node hasn't yet made
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// any observations. It also serves as an upper limit on the error value in
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// case observations cause the error value to increase without bound.
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VivaldiErrorMax float64
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// VivaldiCE is a tuning factor that controls the maximum impact an
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// observation can have on a node's confidence. See [1] for more details.
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VivaldiCE float64
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// VivaldiCC is a tuning factor that controls the maximum impact an
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// observation can have on a node's coordinate. See [1] for more details.
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VivaldiCC float64
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// AdjustmentWindowSize is a tuning factor that determines how many samples
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// we retain to calculate the adjustment factor as discussed in [3]. Setting
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// this to zero disables this feature.
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AdjustmentWindowSize uint
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// HeightMin is the minimum value of the height parameter. Since this
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// always must be positive, it will introduce a small amount error, so
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// the chosen value should be relatively small compared to "normal"
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// coordinates.
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HeightMin float64
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// LatencyFilterSamples is the maximum number of samples that are retained
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// per node, in order to compute a median. The intent is to ride out blips
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// but still keep the delay low, since our time to probe any given node is
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// pretty infrequent. See [2] for more details.
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LatencyFilterSize uint
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// GravityRho is a tuning factor that sets how much gravity has an effect
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// to try to re-center coordinates. See [2] for more details.
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GravityRho float64
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}
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// DefaultConfig returns a Config that has some default values suitable for
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// basic testing of the algorithm, but not tuned to any particular type of cluster.
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func DefaultConfig() *Config {
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return &Config{
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Dimensionality: 8,
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VivaldiErrorMax: 1.5,
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VivaldiCE: 0.25,
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VivaldiCC: 0.25,
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AdjustmentWindowSize: 20,
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HeightMin: 10.0e-6,
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LatencyFilterSize: 3,
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GravityRho: 150.0,
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}
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}
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