Algorithms are the verbs of Mantid. They are the actors. If you want to manipulate your data in any way it will be done through an algorithm. Algorithms operate primarily on data in workspaces. They will normally take one or more workspaces as an input, perform some processing on them and provide an output as another workspace (although it is possible to have multiple outputs).
Each algorithm has a category, a name and a version. The name and version of an algorithm when taken together have to be unique.
A category is a group of algorithms that have some connection in their usage. This is primarily used to make the list of algorithms easier to work with in graphical user interfaces. Example categories include, DataHandling, Diffraction, Muon, Workflow and are currently subcategories of Algorithms category.
The name of an algorithm is what is used to refer to it. This can be different from the class name in C++, as for example if you had two versions of the same algorithm they would have the same name, but would have to have different class names (or at least be in different namespaces).
Mantid allows multiple versions of the same algorithm. These are differentiated by using a single integer as a version number, where a higher version number denotes a more recent version. This allows you to normally use the most recent version of an algorithm but also to access previous versions if you prefer.
Each algorithm will have one or more parameters, known within Mantid as properties, that will control how it performs its processing. These parameters specify both what the inputs and outputs of the algorithm will be as well any other options that alter the processing.
For examples of the parameters of an algorithm, look at the page for one of the example algorithms below.
# where p1,p2 & p3 are values for algorithm "Alg"'s properties
mtd.execute("Alg","p1;p2;p3") # using parameter ordinal position
#or
mtd.execute("Alg","Property1=p1;Property2=p2;Property3=p3") #using parameter names
#or
alg = mtd.createAlgorithm("Alg") # explicitly setting each parameter, then executing
alg.setPropertyValue("Property1","p1")
alg.setPropertyValue("Property2","p2")
alg.setPropertyValue("Property3","p3")
alg.execute()
# Properties of Algorithms can be read (but not written to) through a Python dictionary. So you may do:
print(alg["Property1"])
# prints 'p1'
print(alg["Property2"])
# prints 'p2', etc