### forward model

(model producing potential observable values from parameters)

A **forward model** is a model that takes parameters
and produces observable values. Thus the model
plus a set of parameters constitutes a prediction.
A **backward model** (or **inverse model**) is a model that works in the
reverse direction: given values observed, produces
parameters, which could be characteristics not subject to
observation.

For example, a backward model might be a means of calculating the
abundances of constituents of an extra-solar planet's atmosphere
from transmission spectroscopy data, whereas a forward model
would take assumptions of the abundances and calculate what the
transmission spectroscopy data would be.

Backward models often can be devised using
Markov chain Monte Carlo methods.
Also, a slow backward model can be devised from a forward model
through searching the parameter space.
A backward model that is efficiently calculable can,
in turn, be used in analysis involving many cases of
observed data, e.g., from photometric
surveys of many stars.

(*science,mathematics*)
**Further reading:**

https://astronomy.stackexchange.com/questions/19687/what-does-forward-modeling-mean

https://www.mpia.de/gaia/projects/gsp/ilium

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