.. _cash-flow-model-library:

Cash flow model library
=======================

Besides cash flow tables, costs and incomes associated with operations or tree value models can also be defined with cash flow models; i.e., models predicting the unit price changes over time based on some variables.

All cash flow models have the same set of input parameters:

- *table* -- cash flow table object (for details, see simo.builder.modelbase.cashflowtable.py)
- *date* -- current date as datetime object
- *variables* -- cash flow model input variables
- *parameters* -- cash flow model parameters
- *errors* -- container for returning errors from the model

Below is an example of a stochastic timber assortment price model::

    def random_prices(table, date, variables, parameters, errors):
        ret = True
        index = (1,2)
        
        # the initial year is now fixed to 2008
        n = date.year - 2008 + 1
        
        # load the prices and compute standardized delta (increment), simulate
        # prices for the next n years
        prices, delta_st = _load_prices()
        P = _simulate(prices, delta_st, n, 2)
        
        # store the prices of the last year
        table.set_values(index, PINELOG, P[-1,0])
        table.set_values(index, SPRUCELOG, P[-1,1])
        table.set_values(index, BIRCHLOG1, P[-1,2])
        table.set_values(index, BIRCHLOG2, P[-1,2])
        table.set_values(index, PINEPULP, P[-1,3])
        table.set_values(index, SPRUCEPULP, P[-1,4])
        table.set_values(index, BIRCHPULP1, P[-1,5])
        table.set_values(index, BIRCHPULP2, P[-1,5])
        
        return ret