# getDeltaBLI

Exact BLI of an arbitrarily positioned delta function.

## Syntax

    f = getDeltaBLI(Nx, dx, x, x0)

## Description

`getDeltaBLI` calculates the exact BLI of an arbitrarily positioned delta function. For grid dimensions with an evenly-sampled periodicity, a small Nyquist frequency sinusoid is added. This sinusoid is invisible on grid samples and has zero amplitude when the delta function lies on a grid node. It is important when the evaluation points aren't grid nodes, and when the delta function is off-grid. It serves to ensure conjugate symmetry in the BLI's Fourier transform.

## Inputs

`Nx` | Number of grid points in the relevant Cartesian direction
`dx` | Grid point spacing [m]
`x` | Coordinates at which the BLI is evaluated [m]
`x0` | Coordinate at which the BLI is centred [m]

## Outputs

`f` | Value of the BLI at the specified coordinates

## See Also

`getBLI`