A simple implementation of backwards induction for solving finite-horizon, finite-state stochastic dynamic programs.

## Project description

A simple implementation of backwards induction for solving finite-horizon, finite-space stochastic dynamic programs.

## Installation

stochasticdp is available on PyPI:

`pip install stochasticdp`

## Usage

To initialize a stochastic dynamic program:

`dp = StochasticDP(number_of_stages, states, decisions, minimize)`

where

number_of_stages is an integer

states is a list

decisions is a list

minimize is a boolean

This results in a stochastic dynamic program with stages numbered 0, ..., number_of_stages - 1, and initializes the following dictionaries:

dp.probability, where dp.probability[m, n, t, x] is the probability of moving from state n to state m in stage t under decision x

dp.contribution, where dp.contribution[m, n, t, x] is the immediate contribution of resulting from moving from state n to state m in stage t under decision x

dp.boundary, where dp.boundary[n] is the boundary condition for the value-to-go function at state n

You only need to define probabilities and contributions for transitions that occur with positive probability.

You can use the following helper functions to populate these dictionaries:

```
# This sets dp.probability[m, n, t, x] = p and dp.contribution[m, n, t, x] = c
dp.add_transition(stage=t, from_state=n, decision=x, to_state=m, probability=p, contribution=c)
# This sets dp.boundary[n] = v
dp.boundary(state=n, value=v)
```

To solve the stochastic dynamic program:

`value, policy = dp.solve()`

where

value is a dictionary: value[t, n] is the value-to-go function at stage t and state n

policy is a dictionary: policy[t, n] is the set of optimizers of value[t, n]

## Project details

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