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# 7.5. Fast distance array computation — `MDAnalysis.core.distances`

Fast C-routines to calculate distance arrays from coordinate arrays.

## 7.5.1. Overview

`MDAnalysis.core.distances.``distance_array`(ref, conf[, box[, result]])

  Calculate all distances d_ij between the coordinates ref[i] and conf[j] in the numpy arrays ref and conf. If an orthorhombic box is supplied then a minimum image convention is used before calculating distances.

  If a 2D numpy array of dtype `numpy.float64` with the shape `(len(ref), len(conf))` is provided in result then this preallocated array is filled. This can speed up calculations.

`MDAnalysis.core.distances.``self_distance_array`(ref[, box[, result]])

  Calculate all distances d_ij between atoms i and j in the reference coordinates ref for all N coordinates. Other options as in `distance_array()`.

  If a 1D numpy array of dtype `numpy.float64` with `N*(N-1)/2` elements is provided in result then this preallocated array is filled. This can speed up calculations.

## 7.5.2. Functions

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