Slate (writing) Slate (writing) A slate is a thin piece of hard flat material, such as the rock also called slate, that is used as a medium for writing. The rock is “a metamorphic rock created by the recrystallization of the minerals in shale from clay to parallel-aligned, flat, flake-like minerals such as mica”. The writing slate consisted of a piece of slate, typically either 4x6 inches or 7x10 inches, encased in a wooden frame. A precise date range for writing slates of this type has not been established. Usually, a piece of cloth or slate sponge was used to clean it
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