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Create Multiexperiment Data at the Command Line

Why Create Multiexperiment Data Sets?

You can create iddata objects that contain several experiments. Identifying models for an iddata object with multiple experiments results in an average model.

In the System Identification Toolbox™ product, experiments can either mean data collected during different sessions, or portions of the data collected during a single session. In the latter situation, you can create a multiexperiment iddata object by splitting the data from a single session into multiple segments to exclude bad data, and merge the good data portions.

    Note:   The idfrd object does not support the iddata equivalent of multiexperiment data.

Limitations on Data Sets

You can only merge data sets that have all of the following characteristics:

  • Same number of input and output channels.

  • Same input and output channel names.

  • Same data domain (that is, time-domain data or frequency-domain data).

Entering Multiexperiment Data Directly

To construct an iddata object that includes N data sets, you can use this syntax:

data = iddata(y,u,Ts)

where y, u, and Ts are 1-by-N cell arrays containing data from the different experiments. Similarly, when you specify Tstart, Period, InterSample, and SamplingInstants properties of the iddata object, you must assign their values as 1-by-N cell arrays.

Merging Data Sets

This example shows how to create a multiexperiment iddata object by merging iddata objects, where each contains data from a single experiment or is a multiexperiment data set.

Load iddata objects z1 and z3.

load iddata1
load iddata3

Merge experiments z1 and z3 into the iddata object z.

z = merge(z1,z3)
z =

Time domain data set containing 2 experiments.

Experiment   Samples      Sample Time           
   Exp1         300            0.1              
   Exp2         300            1                
Outputs      Unit (if specified)                
Inputs       Unit (if specified)                

These commands create an iddata object that contains two experiments, where the experiments are assigned default names 'Exp1' and 'Exp2', respectively.

Adding Experiments to an Existing iddata Object

You can add experiments individually to an iddata object as an alternative approach to merging data sets.

For example, to add the experiments in the iddata object dat4 to data, use the following syntax:

data(:,:,:,'Run4') = dat4

This syntax explicitly assigns the experiment name 'Run4' to the new experiment. The Experiment property of the iddata object stores experiment names.

For more information about subreferencing experiments in a multiexperiment data set, see Subreferencing Experiments.

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