Slate industry in Spain Slate industry in Spain 90% of Europes's natural slate used for roofing originates from the slate industry in Spain, with the region of Galicia being the primary source of production. Slate is a fine-grained metamorphic rock that splits into thin, smooth-surfaced layers. Metamorphic rock is rock which was once igneous or sedimentary and has been subsequently subjected to heat and pressure in varying degrees thereby altering its composition, structure and appearance. It is used extensively in the building industry, particularly for roofing tiles. The production of slate is estimated at 4 million tons per year. Galicia is situated on the
K-means++ the "k"-means++ initialization, the algorithm is guaranteed to find a solution that is O(log "k") competitive to the optimal "k"-means solution. To illustrate the potential of the "k"-means algorithm to perform arbitrarily poorly with respect to the objective function of minimizing the sum of squared distances of cluster points to the centroid of their assigned clusters, consider the example of four points in R that form an axis-aligned rectangle whose width is greater than its height. If "k" = 2 and the two initial cluster centers lie at the midpoints of the top and bottom line segments of the rectangle