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 typingthe ob ject 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
Apdm can be thought of as a three-dimensional matrix. Thetypical 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 eachtime 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 rig htconcatenated. Ifthere is an
ambiguity,Xmath assumes tha t the data was bottom concatenated. Keywords can be
used to specify the row and column dimensions of the data matrices.
Toextr act the data again, the function makematrixretur ns 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 canbe
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.