Data Calculator

The Data Calculator dialog

The Data Calculator can be used to perform mathematical operations with datasets to create new datasets. The Data Calculator is accessed in GMS by selecting the Dataset Calculator in the Edit menu. It is accessed in WMS by selecting the Data Calculator command from the Edit menu. The components of the Data Calculator are as follows:

Expression Field

The most important part of the Data Calculator is the Expression field. This is where the mathematical expression is entered. The expression should be formulated using the same rules that are used in formulating equations in a spreadsheet. Parentheses should be used to clearly indicate the preferred order of evaluation. There is no limit on the length of the expression. The operators in the expression should be limited to the operators shown in the bottom-right of the Data Calculator. The operands in the expression should consist of user-defined constants (e.g., 3.14159), or datasets.

List of Datasets

All of the datasets associated with the active object (TIN, Grid, Mesh, or Scatter Point Set) are listed at the top of the Data Calculator. If a transient dataset is highlighted, the time steps are listed on the right side of the Data Calculator. When a dataset is used in an expression, the name of the dataset should NOT be used. Rather, the letter associated with the dataset should be used. For example, if a dataset is listed as "b. head1", the dataset is referenced in the expression simply as "b".

When a transient dataset is used in an expression, either a single time step or the entire sequence of time steps may be used. For example, the expression "abs(d:100)" creates a single (steady state) dataset representing the absolute value of the dataset at time = 100.0. However, the expression "abs(d:all)" creates a transient dataset representing the absolute value of each of the time steps in the original dataset.

Result Name

When an expression is evaluated, a new dataset is created and the name of the new dataset is designated in the Result field.

Operators

The allowable operators are listed in the bottom-right of the dialog. Selecting one of the operator buttons adds the selected operator to the end of the expression. However, the operators can also be typed directly in the expression field. The function of each of the operators is as follows:

Operator	Function
+	Add
-	Subtract
*	Multiply
/	Divide
(	Left parenthesis
)	Right parenthesis
log(x)	The base 10 logarithm of a dataset
ln(x)	The natural logarithm of a dataset
x^a	(x) raised to the (a) power. (x) and (a) can be any mixture of constants and datasets
abs(x)	The absolute value of a dataset
sqrt(x)	The square root of a dataset
avg(x,y)	The average of two datasets
min(x,y)	The minimum of two datasets
max(x,y)	The maximum of two datasets
trunc(x,a,b)	Truncates a dataset (x) so that all values are >= a and <= b

Operating With Transient Datasets

Each argument in the operators listed in the table above may be:

• A steady state (1 time step) dataset
• A specified time step of a transient dataset (i.e., x:#). In this case the # represents the index of the time step as specified in the Time steps window.
• A transient time step (i.e., x:all). These operations are only valid if all arguments/operands have matching time step values. In this case, the result will be a new transient dataset with identical time values as the arguments.

The data calculator supports an alternate format for computing attributes of a transient dataset. This alternate format applies to three of the operators. These operators compute a steady state (single time step) dataset that represents the spatially varied attribute operating on all the time steps.

Operator	Function
ave(x:all)	The average, at each location, of all time steps in the dataset "x"
min(x:all)	The minimum, at each location, of all time steps in the dataset "x"
max(x:all)	The maximum, at each location, of all time steps in the dataset "x"

Compute Button

Once an expression is formulated and a name for the resulting dataset has been specified, the expression can be evaluated by selecting the Compute button. At this point, the dataset is created and the name of the new dataset should appear in the list of datasets.

Restrictions/Rules

The values will be the result of the expression being performed on each set of values of the datasets at each time step. Datasets with point and cell values cannot be mixed in the dataset calculator.

• If no dataset being used in a calculation has activity, the resulting dataset will also not have activity. (See example #1 in the table below)
• In calculations with multiple datasets with one timestep selected, the resulting time step will be 0.0. (See example #4)
• If there is a combination of different selections for time steps and there is at least one dataset with “all time steps” selected, the resulting dataset’s time steps will be that dataset’s time steps. (see example #5)
  • In any such calculations, the calculator will use the single corresponding values array from any datasets with a single time step selected for every corresponding set of values in any datasets with “all time steps” selected. time step in the multiple time step selections.
• All datasets where “all time steps” has been selected must have the same time steps. (See example #9)
• If there is a combination of activity on cells and points between the datasets being used in a calculation, before performing calculations for activity, the calculator will find the point activity from the given cell activity and use that in the activity calculations. (See example #26)

An SMS sample file with the examples in the table can be downloaded here.

Test #	Dataset 1 value location	Dataset 1 activity	Dataset 1 time steps	Dataset 2 value location	Dataset 2 activity	Dataset 2 time steps	Result location	Result activity	Result time steps
1	cells	no activity	1 time step	cells	no activity	1 time step	cells	no activity	1 time step
2	cells	no activity	1 time step	cells	no activity	all time steps	cells	no activity	all time steps
3	cells	no activity	all time steps	cells	no activity	all time steps	cells	no activity	all time steps
4	cells	cells activity	1 time step	cells	cells activity	1 time step	cells	cells activity	1 time step
5	cells	cells activity	1 time step	cells	cells activity	all time steps	cells	cells activity	all time steps
6	cells	cells activity	all time steps	cells	no activity	1 time step	cells	cells activity	all time steps
7	cells	cells activity	all time steps	cells	no activity	all time steps	cells	cells activity	all time steps
8	cells	cells activity	1 time step	cells	no activity	1 time step	cells	cells activity	1 time step
9	cells	cells activity	all time steps	cells	cells activity	all time steps	cells	cells activity	all time steps
10	cells	cells activity	1 time step	cells	no activity	all time steps	cells	cells activity	all time steps
11	points	points activity	1 time step	points	points activity	1 time step	points	points activity	1 time step
12	points	points activity	1 time step	points	points activity	all time steps	points	points activity	all time steps
13	points	cells activity	all time steps	points	no activity	all time steps	points	cells activity	all time steps
14	points	cells activity	all time steps	points	points activity	1 time step	points	points activity	all time steps
15	points	cells activity	all time steps	points	points activity	all time steps	points	points activity	all time steps
16	points	points activity	all time steps	points	points activity	all time steps	points	points activity	all time steps
17	points	no activity	1 time step	points	no activity	1 time step	points	no activity	1 time step
18	points	cells activity	1 time step	points	no activity	1 time step	points	cells activity	1 time step
19	points	cells activity	1 time step	points	cells activity	1 time step	points	cells activity	1 time step
20	points	cells activity	1 time step	points	cells activity	all time steps	points	cells activity	all time steps
21	points	no activity	1 time step	points	no activity	1 time step	points	no activity	1 time step
22	points	no activity	1 time step	points	points activity	all time steps	points	points activity	all time steps
23	points	cells activity	1 time step	points	no activity	all time steps	points	cells activity	all time steps
24	points	no activity	1 time step	points	points activity	1 time step	points	points activity	1 time step
25	points	no activity	all time steps	points	no activity	all time steps	points	no activity	all time steps
26	points	cells activity	1 time step	points	points activity	1 time step	points	points activity	1 time step
27	points	cells activity	1 time step	points	points activity	all time steps	points	points activity	all time steps
28	points	no activity	all time steps	points	points activity	1 time step	points	points activity	all time steps
29	points	no activity	all time steps	points	points activity	all time steps	points	points activity	all time steps
30	points	cells activity	all time steps	points	no activity	1 time step	points	cells activity	all time steps
31	points	cells activity	all time steps	points	cells activity	all time steps	points	cells activity	all time steps

Related Links

• Datasets (GMS)
• Datasets (WMS)
• SMS Data Calculator