generateInitialConfiguration: Produce an initial graph with a given structure
In Albluca/ElPiGraph.R: Elastic principal graph construction

Produce an initial graph with a given structure

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generateInitialConfiguration(X, Nodes, Configuration = "Line",
  DensityRadius = NULL, MaxPoints = 10000, PCADensity = TRUE,
  CenterDataDensity = TRUE)

`X`	numerical 2D matrix, the n-by-m matrix with the position of n m-dimensional points
`Nodes`	integer, number of nodes of the graph
`Configuration`	string, type of graph to return. It should be one of the following value "Line" Points are placed on the 1st principal component between mean-sd and mean+sd "Circle" Points are placed on the the plane induced by the 1st and 2nd principal components. In both dimensions they are placed between mean-sd and mean+sd "Density" Two points are selected randomly in the neighborhood of one of the points with the largest number of neighbour points "DensityProb" Two points are selected randomly in the neighborhood of one of a point randomly selected with a probability proportional to the number of neighbour points "Random" Two points are returned. The first is selected at random, and the second is selected with a probability inversely proportional to thr distance to the 1st point selected
`DensityRadius`	numeric, the radius used to estimate local density. This need to be set when Configuration is equal to "Density"
`MaxPoints`	integer, the maximum number of points for which the local density will be estimated. If the number of data points is larger than MaxPoints, a subset of the original points will be sampled
`PCADensity`	boolean, should PCA be applied to the data before computing the most dense area