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LoadSQW v1¶

Summary ¶

Create a MDEventWorkspace with events in reciprocal space (Qx, Qy, Qz, Energy) from a SQW file.

Properties ¶

Name	Direction	Type	Default	Description
Filename	Input	string	Mandatory	File of type SQW format. Allowed extensions: [‘.sqw’]
OutputWorkspace	Output	MDEventWorkspace	Mandatory	Output IMDEventWorkspace reflecting SQW data read-in.
MetadataOnly	Input	boolean	False	Load Metadata without events.
OutputFilename	Input	string		If the input SQW file is too large to fit in memory, specify an output NXS file. The MDEventWorkspace will be create with this file as its back-end. Allowed extensions: [‘.nxs’]

Description ¶

The algorithm takes every pixel defined in the SQW horace file and converts it into an event.

Only top level binning information is currently taken from DND/Image data. All DND image information is currently ignored and the resulting MDEvent workspace is in the units of \(Q^{-1}\) (SQW dimensions, recalculated to the Crystal? frame, without HKL transformation).

U matrix is set to unity but the B-matrix is read from the SQW and attached to the workspace which may confuse the algorithms which work with MDEventWorkspace produced by Mantid algorithms.

Notes on Horace SQW files ¶

Sqw objects comes in two flavours:

sqw-type
dnd-type

The former has the four main fields fully filled. The fields description is given below. The latter has:

main_header, header, detpar as empty structures (0x0 struct array with no fields)
data.urange and data.pix do not exist.

The dnd-type is created from d0d, d1d,… objects for most algorithms so as to use private methods of sqw objects.

DND-type object can not be currently read or understood by Mantid.

Structure of sqw class with remarks on what is currently used and what is ignored ¶

String started by:
% -- ignored
* -- used

Main_header:
%   main_headerfilename   Name of sqw file that is being read, excluding path
%   main_headerfilepath   Path to sqw file that is being read, including terminating file separator
%   main_headertitle      Title of sqw data structure
%   main_headernfiles     Number of spe files that contribute to the sqw object

Header: (scalar structure, or cellarray of scalar structures if more than one spe file)
%   header{i}.filename   Name of sqw file excluding path
%   header{i}.filepath   Path to sqw file including terminating file separator
%   header{i}.efix       Fixed energy (ei or ef depending on emode)
%   header{i}.emode      Emode=1 direct geometry, =2 indirect geometry, =0 if diffraction ''' Only emode 1 have ever been tried '''
%   header{i}.alatt      Lattice parameters (Angstroms)
%   header{i}.angdeg     Lattice angles (deg)
%   header{i}.cu         First vector defining scattering plane (r.l.u.)
%   header{i}.cv         Second vector defining scattering plane (r.l.u.)
%   header{i}.psi        Orientation angle (rad)
%   header{i}.omega      --|
%   header{i}.dpsi         |  Crystal misorientation description (rad)
%   header{i}.gl           |  (See notes elsewhere e.g. Tobyfit manual
%   header{i}.gs         --|
%   header{i}.en         Energy bin boundaries (meV) in the input spe file [column vector]
%   header{i}.uoffset    Offset of origin of pixel projection axes in r.l.u. and energy i.e. [h; k; l; en] [column vector]
%   header{i}.u_to_rlu   Matrix (4x4) of pixel projection axes in hkle representation
%                      u(:,1) first vector - u(1:3,1) r.l.u., u(4,1) energy etc.
%   header{i}.ulen       Length of pixel projection axes vectors in Ang^-1 or meV [row vector]
%   header{i}.ulabel     Labels of the pixel projection axes [1x4 cell array of character strings]

The pixel projection axes, u1, u2, u3 are the orthonormal vectors of the crystal Cartesian coordinate frame i.e. u1 || a*, u2 in plane of a*, and b*, and u3 || a* x b*. They form the coordinate frame in which the pixel coordinates are stored in data.pix. The pixel projection axes must necessarily be identical for all contributing spe files.

\ **Detpar**\ :
%   detpar.filename    Name of file excluding path
%   detpar.filepath    Path to file including terminating file separator
%   detpar.group       Row vector of detector group number
%   detpar.x2          Row vector of secondary flightpaths (m)
%   detpar.phi         Row vector of scattering angles (deg)
%   detpar.azim        Row vector of azimuthal angles (deg)
%                  (West bank=0 deg, North bank=90 deg etc.)
%   detpar.width       Row vector of detector widths (m)
%   detpar.height      Row vector of detector heights (m)

\ **Data**\ :
%   data.filename   Name of sqw file that is being read, excluding path
%   data.filepath   Path to sqw file that is being read, including terminating file separator
%   data.title      Title of sqw data structure
*   data.alatt      Lattice parameters for data field (Ang^-1)
*   data.angdeg     Lattice angles for data field (degrees)
%   data.uoffset    Offset of origin of projection axes in r.l.u. and energy ie. [h; k; l; en] [column vector]
%   data.u_to_rlu   Matrix (4x4) of projection axes in hkle representation
%                      u(:,1) first vector - u(1:3,1) r.l.u., u(4,1) energy etc.
%   data.ulen       Length of projection axes vectors in Ang^-1 or meV [row vector]
%   data.ulabel     Labels of the projection axes [1x4 cell array of character strings]
%   data.iax        Index of integration axes into the projection axes  [row vector]
%                  Always in increasing numerical order
%                       e.g. if data is 2D, data.iax=[1,3] means summation has been performed along u1 and u3 axes
%   data.iint       Integration range along each of the integration axes. [iint(2,length(iax))]
%                       e.g. in 2D case above, is the matrix vector [u1_lo, u3_lo; u1_hi, u3_hi]
%   data.pax        Index of plot axes into the projection axes  [row vector]
%                  Always in increasing numerical order
%                       e.g. if data is 3D, data.pax=[1,2,4] means u1, u2, u4 axes are x,y,z in any plotting
%                                       2D, data.pax=[2,4]     "   u2, u4,    axes are x,y   in any plotting
%   data.p          Call array containing bin boundaries along the plot axes [column vectors]
%                       i.e. row cell array {data.p{1}, data.p{2} ...} (for as many axes as length of data.pax)
%   data.dax        Index into data.pax of the axes for display purposes. For example we may have
%                  data.pax=[1,3,4] and data.dax=[3,1,2] This means that the first display axis is data.pax(3)=4,
%                  the second is data.pax(1)=1, the third is data.pax(2)=3. The reason for data.dax is to allow
%                  the display axes to be permuted but without the contents of the fields p, s,..pix needing to
%                  be reordered [row vector]
-----> Large data fields, data for MD image
%   data.s          Cumulative signal.  [size(data.s)=(length(data.p1)-1, length(data.p2)-1, ...)]
%   data.e          Cumulative variance [size(data.e)=(length(data.p1)-1, length(data.p2)-1, ...)]
%   data.npix       No. contributing pixels to each bin of the plot axes.
%                  [size(data.pix)=(length(data.p1)-1, length(data.p2)-1, ...)]
----->
*   data.urange     True range of the data along each axis [urange(2,4)]
----> Pixels or events data
*   data.pix        Array containing data for each pixel:
*                  If npixtot=sum(npix), then pix(9,npixtot) contains:
*                   u1      -|
*                   u2       |  Coordinates of pixel in the pixel projection axes
*                   u3       |
*                   u4      -|
*                   irun        Run index in the header block from which pixel came
*                   idet        Detector group number in the detector listing for the pixel
*                   ien         Energy bin number for the pixel in the array in the (irun)th header
*                   signal      Signal array
*                   err         Error array (variance i.e. error bar squared)

data.s is normalized by the number of pixels, as is the variance data.e. For those elements where data.npix==0, data.s=0 and data.e=0

General notes about SQW file assumptions ¶

Parts of the code were written with the idea of generalising functionality at a later stage. However, we can now assume that:

the lattice parameters are all the same for all contributing spe files
the energy offset is zero in cuts
requires that all sqw files that are to be combined have #. each been created from only one spe file #. the same lattice parameters and pixel projection axes as held in the header block #. the same projection axes and offsets, as held in the data block #. the same plot and integration axes, with same bins and integration ranges
the display axes will be taken from the first sqw object in the list to be combined

Usage ¶

Note

To run these usage examples please first download the usage data, and add these to your path. In Mantid this is done using Manage User Directories.

Example - Load 4D workspace form sample SQW file.

# Delete existing workspace if it is already in Mantid as LoadSQW does not support overwriting
# existig workspaces by design
if 'mdws' in mtd:
    DeleteWorkspace('mdws')
#
# Load sample sqw file, present in Mantid unit tests as MD workspace
mdws = LoadSQW('test_horace_reader.sqw');

# Check results
print("Workspace type is:  {}".format(mdws.id()))
print("Workspace has:{0:2} dimensions and contains: {1:4} MD events".format(mdws.getNumDims(),mdws.getNEvents()))

Output:

Workspace type is:  MDEventWorkspace<MDEvent,4>
Workspace has: 4 dimensions and contains:  580 MD events

Categories: AlgorithmIndex | DataHandling\SQW | MDAlgorithms\DataHandling

Source ¶

C++ header: LoadSQW.h

C++ source: LoadSQW.cpp