ibex_bluesky_core.utils

Utilities for plans which are not plan stubs.

Members

NamedReadableAndMovable	Abstract class for type checking that an object is readable, named and movable.
calculate_polarisation	Calculate polarisation or asymmetry, propagating uncertainties.
center_of_mass_of_area_under_curve	Compute the centre of mass of the area under a curve defined by a series of (x, y) points.
centred_pixel	Given a centre and range, return a contiguous range of pixels around the centre, inclusive.
get_pv_prefix	Return the PV prefix for the current instrument.
is_matplotlib_backend_qt	Return True if matplotlib is using a qt backend.

class ibex_bluesky_core.utils.NamedReadableAndMovable(*args, **kwargs)

Bases: Readable[Any], NamedMovable[Any], Protocol

Abstract class for type checking that an object is readable, named and movable.

ibex_bluesky_core.utils.calculate_polarisation(a: T, b: T, alpha: float = 1.0) → T

Calculate polarisation or asymmetry, propagating uncertainties.

The value returned by this function is:

\[f(a, b, \alpha) = \frac{a - \alpha b}{a + \alpha b}\]

Where \(a\) and \(b\) are the two input scipp variables, which may have corresponding variances, and \(\alpha\) is an optional scalar (float). If \(\alpha\) is not provided, it defaults to 1.

The variances are propagated using the partial derivatives of \(f\) with respect to \(a\) and \(b\):

\[ \begin{align}\begin{aligned}\frac{\partial f}{\partial a} = \frac{2 b \alpha}{(a + b \alpha)^2}\\\frac{\partial f}{\partial b} = \frac{-2 a \alpha}{(a + b \alpha)^2}\\\sigma_f^2 = (\frac{\partial f}{\partial a})^2 \sigma_a^2 + (\frac{\partial f}{\partial b})^2 \sigma_b^2\end{aligned}\end{align} \]

Note

\(\alpha\) is a scalar constant and is assumed not to have a variance.

On SANS instruments (e.g. LARMOR) and reflectometry instruments (e.g. POLREF), \(a\) and \(b\) correspond to intensity in different DAE periods (before/after switching a flipper) and the output is interpreted as a neutron polarisation ratio. \(\alpha\) is fixed at 1.

On muon instruments, \(a\) and \(b\) correspond to measuring from forward/backward detector banks, and the output is interpreted as a muon asymmetry. \(\alpha\) will not necessarily be 1.

Parameters:

• a – scipp Variable or DataArray

• b – scipp Variable or DataArray

• alpha – Optional scalar, defaults to 1.

Returns:

Polarisation or asymmetry as a scipp Variable or DataArray

ibex_bluesky_core.utils.center_of_mass_of_area_under_curve(x: ndarray[tuple[Any, ...], dtype[float64]], y: ndarray[tuple[Any, ...], dtype[float64]]) → tuple[float, float]

Compute the centre of mass of the area under a curve defined by a series of (x, y) points.

The “area under the curve” is a shape bounded by: - min(y), along the bottom edge - min(x), on the left-hand edge - max(x), on the right-hand edge - straight lines joining (x, y) data points to their nearest neighbours along the x-axis, along the top edge

This is implemented by geometric decomposition of the shape into a series of trapezoids, which are further decomposed into rectangular and triangular regions.

Returns a tuple of the centre of mass and the total area under the curve.

ibex_bluesky_core.utils.centred_pixel(centre: int, pixel_range: int) → list[int]

Given a centre and range, return a contiguous range of pixels around the centre, inclusive.

ie. a centre of 50 with a range of 3 will give [47, 48, 49, 50, 51, 52, 53]

Parameters:

• centre (int) – The centre pixel number.

• pixel_range (int) – The range of pixels either side to surround the centre.

Returns a list of pixel numbers.

ibex_bluesky_core.utils.get_pv_prefix() → str

Return the PV prefix for the current instrument.

ibex_bluesky_core.utils.is_matplotlib_backend_qt() → bool

Return True if matplotlib is using a qt backend.