### 3.4.7. Using the CFX-Interpolator to Calculate Difference Variables

The main use of the CFX-Interpolator is in providing initial conditions from existing results file for use in a new run. However, you can also use the CFX-Interpolator to compare two results files. When used in this mode, you provide it with a two results files, and the CFX-Interpolator writes a new set of variables into one of the results files of the form `Pressure.Difference`, which is the difference between the pressures in the two results files. These difference variables can then be viewed in CFD-Post. For a description of the general variable syntax, see Quantitative CEL Functions in ANSYS CFX in the CFX Reference Guide.

For Release 12.0 and later, this use of the CFX-Interpolator is largely superseded by the ability of CFD-Post to calculate difference variables and to compare two results files in a more flexible way. For details, see Case Comparison in the CFD-Post User's Guide.

The functionality to calculate difference variables using the CFX-Interpolator is available either through Tools > Interpolate Results in the CFX-Solver Manager, or through the `cfx5interp` command on the command line. See Using the Command Line to Interpolate Results in the CFX-Solver Manager User's Guide for details. See Calculating Difference Variables in the CFD-Post User's Guide for details on how the difference of vector variables such as `Velocity` is calculated.

For moving mesh cases, the difference variables are calculated using the final mesh positions.

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