Importing Frequency Domain Data

This dialog is used to enter input and output signals or frequency response signals into the GUI and to associate the signals with relevant information.

First there is a choice between different cases of signals, controlled by the popup-menu Data Format for Signals:

Fredquency Domain Signals
This is the case where the input and output signals are given in the frequency domain (Fourier transforms).
Frequency Function given as a complex-valued response
This is the case where the frequency response of a model y = G u + H e is given as the complex valued frequency function G(exp(iwT)). Here w is a vector of frequences and T is the sampling interval. For continuous time models the frequency function is G(iw). Optionally, the output disturbance spectrum v |H|^2 (where v is the variance of the white noise e) could also be given.
Frequency Function given as amplitude and phase data.
This is the same case as above, except that G(iw) is given as Amplitude = abs(G(iw)) and Phase = arg(G(iw)) (in degrees) instead of as complex values.

Entering the signals

Enter valid MATLAB expressions in the Workspace Variable edit boxes. The expressions should evaluate to either a column vector or a matrix. The frequency vector must have the same number of rows as the signals.

A valid expression is, for example,
[temp(234:500) current(234:500)]
where temp and current are column vector variables in the MATLAB workspace.

For single-input-single-output data, all signals are vectors. For a data set with NY outputs, NU inputs and NF frequencies, the frequency function data are NY-by-Nu-by-NF arrays (applies both to Frequency Function, Aplitude and Phase) while Spectrum (if entered) is a NY-by-Ny-by-NF array. For the input-output data case, the signals are NU-by-NF and NY-by-NF matrices, respectively.

Entering More Information

Optionally enter any string in the Data name: edit box. The data set will be labeled with the name in the ident window.

The Sampling Interval Information is essential also for frequency domain data. It will e.g. decide the Nyquist frequency. Enter 0 (zero) for continuous time data.

Enter the Frequency Unit as 'Hz' or 'rad/s' for the unit in which the frequency vector was expressed. Note the inside the GUI, the frequency unit will always be rad/s, but you will be able to choose frequency axis in plots as you like.

Pressing the More button gives access to more properies to associate the data with,

The channel names will follow the data, and be the basis for subselecting channels etc. Default names are 'y1', 'y2', ... 'u1', 'u2' etc. The noise sources will be automatically named for for the corresponding output: 'e@yname' is the name of the disturbance that is additive to the output with name 'yname'.

The names are entered without quotes, separed by commas. The number of names must equal the number of channels.

Units for the measured variables can be given, if desired. These are used only for plot information. Enter as comma separated strings. (No quotes.)

Enter any text into the edit box at the bottom. The notes will remain associated with the data and any models which are estimated from it.

Press the button Less to remove the extra page.

Press Import to enter the data set into the ident Data board.

Press Reset to return all edit boxes to their default values.

If you have a variable in the workspace that is in the IDDATA or IDFRD formats (type HELP IDDATA or HELP IDFRD) it is more efficient to use the Import Data Object dialog. This is opened by typing the hotkey d in the ident window or by selecting this item in the Data popupmenu.

Help topics.

(file iduiimp3.htm)