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74 CHAPTER 3. FUNCTIONAL DESCRIPTION OF Xµ
Because the dynamic system is a built-in data object, the label information will be
displayed by simply typing the object name (sys in the above) or appending a question
mark to the statement. The core function commentof is used to read the comment
attached to a specified variable.
3.2.2 pdms
A pdm can be thought of as a three-dimensional matrix. The typical control uses are
time or frequency responses, where the domain variable (the third dimension) is time or
frequency. The frequency response of a multiple-input, multiple-output (MIMO) system
is a complex valued matrix at each frequency. A time response of a multiple-output
system is a real valued vector at each time step.
As we would expect, there is a core function for constructing pdms from the raw data:
pdm. The data matrices can be either bottom or right concatenated. If there is an
ambiguity, Xmath assumes that the data was bottom concatenated. Keywords can be
used to specify the row and column dimensions of the data matrices.
To extract the data again, the function makematrix returns the matrix data in right
concatenated form. The domain of a pdm is obtained with the function domain.
# Make a pdm with 2 values in the domain
mat1 = random(2,2)
mat2 = -1*random(2,2)
dom = [1;1+pi]
pdm1 = pdm([mat1;mat2],dom)
# Extract back the data and the domain
dom = domain(pdm1)
data = makematrix(pdm1)
The pdm data object also contains row, column and domain labels. These can be
appended with the pdm command in exactly the same manner as the Dynamic System
labels illustrated above. Refer to the Xmath Basics manual for graphical illustration and
further details about pdms.