### 1.11.1. Adaption Criteria

This section describes how the adaption criteria are calculated for each mesh edge.

- If the adaption criteria method is Solution Variation, then the adaption criteria, , for a given mesh edge of length is calculated as:

  | (1–275)

  where is the adaption variable (such as density, pressure, and so on), is the global range of the variable over all the nodes (excluding those on wall boundary conditions for turbulent flow), is the difference between at one end of the edge and the other end, and is a scalar for adaption variable to scale all the to take values between 0 and 1.

- If the adaption criteria method is `Variation * Edge Length`, then the adaption criteria for a given mesh edge of length is calculated as:

  | (1–276)

  where: is the global range of the adaption variable over all the nodes (excluding those on wall boundary conditions for turbulent flow), is the difference between at one end of the edge and the other end, and is a length chosen to scale all the to take values between 0 and 1.

- If you select more than one solution variable, then the adaption criteria are calculated for each variable at each edge, and the sum over all adaption variables is used.

- If you specify the adaption criteria to be an expression, then the expression is evaluated at each node, and the calculation of the adaption criteria follows as if this were another solution variable.

The edges that have the largest adaption criteria are marked for refinement, providing that this would not result in mesh edges that were shorter than the Minimum Edge Length, if this was specified.

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