### 15.5.9. inside

The `inside` CEL function is essentially a step function variable, defined to be unity within a subdomain and zero elsewhere. This is useful for describing different initial values or fluid properties in different regions of the domain. It is similar to the CEL subdomain variable, but allows a specific 2D or 3D location to be given. For example, `273 [K] * inside()@Subdomain 1` has a value of 273 [K] at points in Subdomain 1 and 0 [K] elsewhere. The location does not need to be a subdomain, but can be any 2D or 3D named sub-region of the physical location on which the expression is evaluated. For immersed solids simulations, the location can also be a specific immersed solid domain, and the inside function will be updated automatically at the beginning of each time step.

    inside()@<Location>

where:

- `<Location>` is any 2D or 3D named sub-region of the physical location on which the expression is evaluated.

- `<Location>` can also be an immersed solid domain on which the expression is evaluated dynamically.

Note: The `inside` CEL function is not available in CFD-Post.

#### 15.5.9.1. Tools > Command Editor Example

    >calculate inside, <Location>

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