Documentation

ltiblock.gain

Tunable static gain block

Syntax

blk = ltiblock.gain(name,Ny,Nu)
blk = ltiblock.gain(name,G)

Description

Model object for creating tunable static gains. ltiblock.gain lets you parametrize tunable static gains for parameter studies or for automatic tuning with Robust Control Toolbox™ tuning commands such as systune or looptune.

ltiblock.gain is part of the Control Design Block family of parametric models. Other Control Design Blocks includeltiblock.pid, ltiblock.ss, and ltiblock.tf.

Construction

blk = ltiblock.gain(name,Ny,Nu) creates a parametric static gain block named name. This block has Ny outputs and Nu inputs. The tunable parameters are the gains across each of the Ny-by-Nu I/O channels.

blk = ltiblock.gain(name,G) uses the double array G to dimension the block and initialize the tunable parameters.

Input Arguments

name

String specifying the block Name. (See Properties.)

Ny

Non-negative integer specifying the number of outputs of the parametric static gain block blk.

Nu

Non-negative integer specifying the number of inputs of the parametric static gain block blk.

G

Double array of static gain values. The number of rows and columns of G determine the number of inputs and outputs of blk. The entries G are the initial values of the parametric gain block parameters.

Properties

Gain

Parametrization of the tunable gain.

blk.Gain is a param.Continuous object. For general information about the properties of the param.Continuous object blk.Gain, see the param.Continuousparam.Continuous object reference page.

The following fields of blk.Gain are used when you tune blk using hinfstruct:

FieldDescription
ValueCurrent value of the gain matrix. For a block that has Ny outputs and Nu inputs, blk.Gain.Value is a Ny-by-Nu matrix.
If you use the G input argument to create blk, blk.Gain.Value initializes to the values of G. Otherwise, all entries of blk.Gain.Value initialize to zero.
hinfstruct tunes all entries in blk.Gain.Value except those whose values are fixed by blk.Gain.Free.
Default: Array of zero values.
FreeArray of logical values determining whether the gain entries in blk.Gain.Value are fixed or free parameters.
  • If blk.Gain.Free(i,j) = 1, then blk.Gain.Value(i,j) is a tunable parameter.

  • If blk.Gain.Free(i,j) = 0, then blk.Gain.Value(i,j) is fixed.


Default: Array of 1 (true) values.
MinimumMinimum value of the parameter. This property places a lower bound on the tuned value of the parameter. For example, setting blk.Gain.Minimum = 1 ensures that all entries in the gain matrix have gain greater than 1.
Default: -Inf.
MaximumMaximum value of the parameter. This property places an upper bound on the tuned value of the parameter. For example, setting blk.Gain.Maximum = 100 ensures that all entries in the gain matrix have gain less than 100.
Default: Inf.

Ts

Sampling time. For continuous-time models, Ts = 0. For discrete-time models, Ts is a positive scalar representing the sampling period. This value is expressed in the unit specified by the TimeUnit property of the model. To denote a discrete-time model with unspecified sampling time, set Ts = -1.

Changing this property does not discretize or resample the model. Use c2d and d2c to convert between continuous- and discrete-time representations. Use d2d to change the sampling time of a discrete-time system.

Default: 0 (continuous time)

TimeUnit

String representing the unit of the time variable. This property specifies the units for the time variable, the sampling time Ts, and any time delays in the model. Use any of the following values:

  • 'nanoseconds'

  • 'microseconds'

  • 'milliseconds'

  • 'seconds'

  • 'minutes'

  • 'hours'

  • 'days'

  • 'weeks'

  • 'months'

  • 'years'

Changing this property has no effect on other properties, and therefore changes the overall system behavior. Use chgTimeUnit to convert between time units without modifying system behavior.

Default: 'seconds'

InputName

Input channel names. Set InputName to a string for single-input model. For a multi-input model, set InputName to a cell array of strings.

Alternatively, use automatic vector expansion to assign input names for multi-input models. For example, if sys is a two-input model, enter:

sys.InputName = 'controls';

The input names automatically expand to {'controls(1)';'controls(2)'}.

You can use the shorthand notation u to refer to the InputName property. For example, sys.u is equivalent to sys.InputName.

Input channel names have several uses, including:

  • Identifying channels on model display and plots

  • Extracting subsystems of MIMO systems

  • Specifying connection points when interconnecting models

Default: Empty string '' for all input channels

InputUnit

Input channel units. Use InputUnit to keep track of input signal units. For a single-input model, set InputUnit to a string. For a multi-input model, set InputUnit to a cell array of strings. InputUnit has no effect on system behavior.

Default: Empty string '' for all input channels

InputGroup

Input channel groups. The InputGroup property lets you assign the input channels of MIMO systems into groups and refer to each group by name. Specify input groups as a structure. In this structure, field names are the group names, and field values are the input channels belonging to each group. For example:

sys.InputGroup.controls = [1 2];
sys.InputGroup.noise = [3 5];

creates input groups named controls and noise that include input channels 1, 2 and 3, 5, respectively. You can then extract the subsystem from the controls inputs to all outputs using:

sys(:,'controls')

Default: Struct with no fields

OutputName

Output channel names. Set OutputName to a string for single-output model. For a multi-output model, set OutputName to a cell array of strings.

Alternatively, use automatic vector expansion to assign output names for multi-output models. For example, if sys is a two-output model, enter:

sys.OutputName = 'measurements';

The output names to automatically expand to {'measurements(1)';'measurements(2)'}.

You can use the shorthand notation y to refer to the OutputName property. For example, sys.y is equivalent to sys.OutputName.

Output channel names have several uses, including:

  • Identifying channels on model display and plots

  • Extracting subsystems of MIMO systems

  • Specifying connection points when interconnecting models

Default: Empty string '' for all input channels

OutputUnit

Output channel units. Use OutputUnit to keep track of output signal units. For a single-output model, set OutputUnit to a string. For a multi-output model, set OutputUnit to a cell array of strings. OutputUnit has no effect on system behavior.

Default: Empty string '' for all input channels

OutputGroup

Output channel groups. The OutputGroup property lets you assign the output channels of MIMO systems into groups and refer to each group by name. Specify output groups as a structure. In this structure, field names are the group names, and field values are the output channels belonging to each group. For example:

sys.OutputGroup.temperature = [1];
sys.InputGroup.measurement = [3 5];

creates output groups named temperature and measurement that include output channels 1, and 3, 5, respectively. You can then extract the subsystem from all inputs to the measurement outputs using:

sys('measurement',:)

Default: Struct with no fields

Name

System name. Set Name to a string to label the system.

Default: ''

Notes

Any text that you want to associate with the system. Set Notes to a string or a cell array of strings.

Default: {}

UserData

Any type of data you wish to associate with system. Set UserData to any MATLAB® data type.

Default: []

Examples

Create a 2-by-2 parametric gain block of the form

[g100g2]

where g1 and g2 are tunable parameters, and the off-diagonal elements are fixed to zero.

blk = ltiblock.gain('gainblock',2,2);  % 2 outputs, 2 inputs
blk.Gain.Free = [1 0; 0 1];    % fix off-diagonal entries to zero

All entries in blk.Gain.Value initialize to zero. Initialize the diagonal values to 1 as follows.

blk.Gain.Value = eye(2);    % set diagonals to 1

Create a two-input, three-output parametric gain block and initialize all the parameter values to 1.

To do so, create a matrix to dimension the parametric gain block and initialize the parameter values.

G = ones(3,2);
blk = ltiblock.gain('gainblock',G);

Create a 2–by-2 parametric gain block and assign names to the inputs.

blk = ltiblock.gain('gainblock',2,2)   % 2 outputs, 2 inputs 
blk.InputName = {'Xerror','Yerror'}    % assign input names

More About

expand all

Tips

  • Use the blk.Gain.Free field of blk to specify additional structure or fix the values of specific entries in the block. To fix the gain value from input i to output j, set blk.Gain.Free(i,j) = 0. To allow hinfstruct to tune this gain value, set blk.Gain.Free(i,j) = 1.

  • To convert an ltiblock.gain parametric model to a numeric (non-tunable) model object, use model commands such as tf, zpk, or ss.

Was this topic helpful?