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## Changing the order of operators

Sometimes when you've applied several operators, it is useful to change the order of the operators around. For example, you might want to apply a Slice operator before a Reflect operator instead of after it so you can reduce the amount of data that VisIt must process in order to draw your plot. The order in which operators are applied often has a significant impact on the visualization. Using the previous example, suppose a plot is sliced before it is reflected. The resulting visualization is likely to have a reflected slice of the original data. If the order of the operators was reversed so the Reflect operator came first, the Slice operator's slice plane might not intersect the reflected data in the same way, which could result in a totally different looking visualization.

Figure 6

You must expand a plot list entry in order to change the order of its operators. Once the plot list entry is expanded, each operator is listed in the order in which they were applied and each operator has small buttons to the right of the its name that allow you to move the operator up or down in the pipeline. To move an operator closer to the database so it is executed before it would have been executed before, click on the Up button next to an operator's name. Moving the operator closer to the database in the pipeline is called demoting the operator. If you click the Down button next to an operator's name, that operator is moved to a later stage of the pipeline. Moving an operator to a later stage of the pipeline is known as promoting the operator since the operator appears closer to the plot in the expanded plot entry. Operators in the plot list entry that can only be moved in one direction have only the Up button or the Down button while operators in the middle of the pipeline have both the Up button and the Down button.