A domain is a set of all independent variables that make a function meaningful. It can also be specified artificially, but it must be meaningful. For example, the definition fields of linear function, exponential function and sine and cosine function are all real numbers, and the definition fields of inverse proportional function are all real numbers except 0. However, a function corresponds to a domain, and if it is not specified, it defaults to the set of all independent variables that make the function meaningful. Range is a set of function values in the definition domain, which is generally related to the definition domain.