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Description
-----------

Symmetrise takes a matrix workspace containing asymmetric data and makes
it symmetrical around x=0 by reflecting a given section of the right hand
side (positive) on the left hand side (negative).

Two values, XMin and XMax, are chosen to specify the section of the positive
side of the curve to be reflected onto the negative side, the sample curve
is cropped at XMax ensuring that the symmetrised curve has a symmetrical X
range.


Usage
-----

**Example - Running Symmetrise on an asymmetric workspace.**

.. testcode:: ExSymmetriseSimple

    import numpy as np

    # create an asymmetric line shape
    def rayleigh(x, sigma):
      return (x / sigma ** 2) * np.exp(-x ** 2 / (2 * sigma ** 2))

    data_x = np.arange(0, 10, 0.01)
    data_y = rayleigh(data_x, 1)

    sample_ws = CreateWorkspace(data_x, data_y)
    sample_ws = ScaleX(sample_ws, -1, "Add")  # centre the peak over 0

    symm_ws = Symmetrise(InputWorkspace=sample_ws, XMin=0.05, XMax=8.0)

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