3.5

MD Histogram Workspace

The MD Histogram Workspace[MDHistoWorkspace] is a simple multi-dimensional workspace. In contrast to the MDWorkspace, which contains points in space, the MDHistoWorkspace consists of a signal and error spread around space on a regular grid.

In a way, the MDHistoWorkspace is to a MDWorkspace is what the Workspace2D is to the EventWorkspace.

Creating a MDHistoWorkspace

MDHistoWorkspaces typically have 3 or 4 dimensions, although they can be created in up to 9 dimensions.

Viewing a MDHistoWorkspace

  • MDHistoWorkspaces can be created and visualized directly within Paraview and the Vates Simple Interface when rebinning along a regular grid.
  • You can right-click on the workspace and select:
    • Plot MD: to perform a 1D plot of the signal in the workspace (only works on 1D MDHistoWorkspaces).
    • Show Slice Viewer: to open the Slice Viewer, which shows 2D slices of the multiple-dimension workspace.

Arithmetic Operations

The following algorithms allow you to perform simple arithmetic on the values:

These arithmetic operations propagate errors as described here. The formulas used are described in each algorithm’s wiki page.

The basic arithmetic operators are available from python. For example:

# Get two workspaces
A = mtd['workspaceA']
B = mtd['workspaceB']
# Creating a new workspace
C = A + B
C = A - B
C = A * B
C = A / B
# Modifying a workspace in-place
C += A
C -= A
C *= A
C /= A
# Operators with doubles
C = A * 12.3
C *= 3.45

Compound arithmetic expressions can be made, e.g:

E = (A - B) / (C - D)

Boolean Operations

The MDHistoWorkspace can be treated as a boolean workspace. In this case, 0.0 is “false” and 1.0 is “true”.

The following operations can create a boolean MDHistoWorkspace:

These operations can combine/modify boolean MDHistoWorkspaces:

These boolean operators are available from python. Make sure you use the bitwise operators: & | ^ ~ , not the “word” operators (and, or, not). For example:

# Create boolean workspaces by comparisons
C = A > B
D = B < 12.34
# Combine boolean workspaces using not, or, and, xor:
not_C = ~C
C_or_D = C | D
C_and_D = C & D
C_xor_D = C ^ D
C |= D
C &= D
C ^= D
# Compound expressions can be used:
D = (A > 123) & (A > B) & (A < 456)

Using Boolean Masks

The SetMDUsingMask algorithm allows you to modify the values in a MDHistoWorkspace using a mask created using the boolean operations above. See the algorithm wiki page for more details.

Category: Concepts