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
Change of variables (PDE) Change of variables (PDE) Often a partial differential equation can be reduced to a simpler form with a known solution by a suitable change of variables. The article discusses change of variable for PDEs below in two ways: For example, the following simplified form of the Black–Scholes PDE is reducible to the heat equation by the change of variables: in these steps: Advice on the application of change of variable to PDEs is given by mathematician J. Michael Steele: Suppose that we have a function formula_24 and a change of variables formula_25 such that there exist functions formula_26 such that