Target Variables

Your application utilizes the concept of target variable to define optimization constraints wherever they are needed; for example:

Pit Optimizer in “blending” mode uses target variables to formulate blending targets.
Scheduler uses target variables to formulate scheduling targets.
MAO and MFO use target variables to formulate “quality targets” and “global targets”.

Rates and Ratios

The Rate variable has the form:

V = A*x + B*y + C*z + ..

The Ratio variable has the form:

V = (A*x + B*y + C*z + ̤ )/(D*x + E*y + F*z + ..)

Where A, B, C, D, E, F etc. are user defined coefficients and x, y, z etc. are model variables. The model variable sets may differ depending on the context; for example, they represent mass of non monetary Economic Model fields in Pit Optimizer and Scheduler, element grades in MAO quality targets and user defined quantities in MAO global targets.

Note: (A*x + B*y + C*z + .. ) is called the Numerator and (D*x + E*y + F*z +..) is called Denominator.

Target and Limits

The purpose of optimization is to optimize an objective keeping the target variables within certain limits or, sometimes, exactly at a target value. You may be required to define one, two or all three of the following parameters, any one of which may vary over time:

Target (Ideal Value)
Lower Limit
Upper Limit

Which parameters are required depends on the context:

Pit Optimizer’s blending: upper and lower limits must be defined.
Scheduler – All three parameters must be defined although only the Target of the target variable chosen as the “primary optimization objective” will actually be used.
MAO/MFO provide the following options for both quality targets and global targets:
- Define the Target: the target variable must stay exactly at the target value (equality constraint); the limit parameters will be ignored so you need not define them.
- Define the Lower Limit: the target variable must stay above the limit (greater than or equal to constraint); Target must remain blank, the Upper Limit may or may not be defined.
- Define the Upper Limit: the target variable must stay below the limit (less than or equal to constraint); Target must remain blank, the Lower Limit may or may not be defined.