An inverse function is a concept of mathematics. A function will calculate some output formula_1, given some input formula_2. This is usually written formula_3. The inverse function does the reverse. Let's say formula_4 is the inverse function of formula_5, then formula_6. Or otherwise put, formula_7. An inverse function to formula_5 is usually called formula_9. It is not to be confused with formula_10, which is a reciprocal function.