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An activity is an equation unit within a domain. It defines a relationship among variables — for example, the relationship between a loan amount, an interest rate, a term, and a monthly payment. Activities are the building blocks of a domain. A domain is typically made up of many activities, connected through the variables they share.

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What an activity defines

  • An equation — the mathematical relationship, written in TrueMath’s writing equations.
  • The variables it relates — and, for each, whether it is calculable by this activity (that is, whether the activity can solve for it).
  • A title and description — so the activity’s purpose is clear to the people reading the domain.

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Solving in more than one direction

An activity is not locked to a single input-output direction. Given a payment, a rate, and a term, an activity can solve for the loan amount; given a target payment, it can solve for the affordable purchase price. The author defines which of an activity’s variables are calculable — the ones it may solve for; within that set, which variable is actually computed depends on the values you provide and what you ask to solve for. This is what lets a domain answer what-if questions naturally rather than only running a fixed calculation.

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Activity state

An activity can be active or disabled. Disabled activities remain part of the domain definition but are not used when running calculations.
You define activities and their equations when authoring a domain. To see the activities in a published domain, use GET /v1/domains/:id/activities.