Oracle9i OLAP Services Developer's Guide to the OLAP DML Release 1 (9.0.1) Part Number A8672001 

Working with Models, 6 of 8
When you run a model, you should keep these points in mind:
Several OLAP DML functions make it easy for you to use data from past or future time periods. For example, the LAG function returns data from a specified previous time period, and the LEAD function returns data from a specified future period. The OLAP DML Reference lists some builtin functions that are useful in analyzing financial data.
When you run a model that uses past or future data in its calculations, you must make sure that your solution variable contains the necessary past or future data. For example, a model might contain an assignment statement (that is, the = command) that bases an estimate of the REVENUE line item for the current month on the REVENUE line item for the previous month.
dimension line month . . . revenue = lag(revenue, 1, month) * 1.05
If the MONTH dimension is limited to APR96 to JUN96 when you run the model, then you must be sure that the solution variable contains REVENUE data for MAR96.
If your model contains a LEAD function, then your solution variable must contain the necessary future data. For example, if you want to calculate data for the months of April through June of 1996, and if the model retrieves data from one month in the future, then the solution variable must contain data for July 1996 when you run the model.
An iterative method is used to solve the equations in a simultaneous block. In each iteration, a value is calculated for each equation, and compares the new value to the value from the previous iteration. If the comparison falls within a specified tolerance, then the equation is considered to have converged to a solution. If the comparison exceeds a specified limit, then the equation is considered to have diverged.
If all the equations in the block converge, then the block is considered solved. If any equation diverges or fails to converge within a specified number of iterations, then the solution of the block (and the model) fails and an error occurs.
You can use OLAP DML options to exercise control over the solution of simultaneous equations. For example, you can specify the solution method to use, the factors to use in testing for convergence and divergence, the maximum number of iterations to perform, and the action to take when the = command diverges or fails to converge. For more information about the options, see the entry for the MODEL command in OLAP DML Reference.

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