|Definition:|| function for which both the argument and the value are functions|
Note 1 to entry: An example of transformation is the Fourier transformation, where the argument is a function of time and the value is the Fourier transform of this function. When the argument, the value, or both, are ordered set of entities, a linear transformation is often represented by a matrix.
Note 2 to entry: For historical reasons, some transformations are called operators, e.g. nabla operator (IEC 60050-102, 102-05-18).