Constant (Simulink Reference)

Generate a constant value

Library

Sources

Description

The Constant block generates a real or complex constant value. The block generates scalar (1x1 2-D array), vector (1-D array), or matrix (2-D array) output, depending on the dimensionality of the Constant value parameter and the setting of the Interpret vector parameters as 1-D parameter.

The output of the block has the same dimensions and elements as the Constant value parameter. If you specify a vector for this parameter, and you want the block to interpret it as a vector (i.e., a 1-D array), select the Interpret vector parameters as 1-D parameter; otherwise, the block treats the Constant value parameter as a matrix (i.e., a 2-D array).

Data Type Support

By default, the Constant block outputs a signal whose data type and complexity are the same as that of the block's Constant value parameter. However, you can specify the output to be any supported data type supported by Simulink, including fixed-point data types.

For a discussion on the data types supported by Simulink, refer to Data Types Supported by Simulink in the Using Simulink documentation.

Parameters and Dialog Box

The Main pane of the Constant block dialog appears as follows:

Opening this dialog box causes a running simulation to pause. See Changing Source Block Parameters in the online Simulink documentation for details.

Constant value: Specify the constant value output by the block. You can enter any MATLAB expression in this field, including the Boolean keywords, true or false, that evaluates to a matrix value. The Constant value parameter is converted from its data type to the specified output data type offline using round-to-nearest and saturation.
Interpret vector parameters as 1-D: If you select this check box, the Constant block outputs a vector of length N if the Constant value parameter evaluates to an N-element row or column vector, i.e., a matrix of dimension 1xN or Nx1.
Sample time: Specify the interval between times that the Constant block's output can change during simulation (e.g., as a result of tuning its Constant value parameter). The default sample time is inf, i.e., the block's output can never change. This setting speeds simulation and generated code by avoiding the need to recompute the block's output. See Specifying Sample Time in the online documentation for more information.

The Signal data types pane of the Constant block dialog appears as follows:

Output data type mode: Specify how the data type of the output is designated. The data type can be inherited through backpropagation, or can be designated in the Constant value parameter, for example int8(29). You can also choose a built-in data type from the list. If you choose Specify via dialog, the following parameters become visible.
Output data type: Specify any data type, including fixed-point data types. This parameter is only visible you select Specify via dialog for the Output data type mode parameter.
Output scaling mode: Specify how the scaling of the output is designated. The output can be automatically scaled to maintain best vector-wise precision without overflow, or you can choose to specify the scaling in the dialog via the Output scaling value parameter. This parameter is only visible if you select Specify via dialog for the Output data type mode parameter.
Output scaling value: Set the output scaling using binary point-only or [Slope Bias] scaling. This parameter is only visible if you select Specify via dialog for the Output data type mode parameter and Use specified scaling for the Output Scaling Mode parameter.

Characteristics

Direct Feedthrough
N/A

Sample Time
Specified in the Sample time parameter

Scalar Expansion
No

Dimensionalized
Yes

Zero Crossing
No

Direct Feedthrough	N/A
Sample Time	Specified in the Sample time parameter
Scalar Expansion	No
Dimensionalized	Yes
Zero Crossing	No

Configurable Subsystem Cosine