Simulink Reference

Product

Multiply or divide inputs

Library

Math Operations

Description

The Product block performs multiplication or division of its inputs.

This block produces outputs using either element-wise or matrix multiplication, depending on the value of the Multiplication parameter. You specify the operations with the Number of inputs parameter. Multiply(*) and divide(/) characters indicate the operations to be performed on the inputs:

• If there are two or more inputs, then the number of characters must equal the number of inputs. For example, "*/*" requires three inputs. For this example, if the Multiplication parameter is set to Element-wise, the block divides the elements of the first (top) input by the elements of the second (middle) input, and then multiplies by the elements of the third (bottom) input. In this case, all nonscalar inputs to this block must have the same dimensions.

• If, however, the Multiplication parameter is set to Matrix, the block output is the matrix product of the inputs marked "*" and the inverse of inputs marked "/", with the order of operations following the entry in the Number of inputs parameter. The dimensions of the inputs must be such that the matrix product is defined.

Note    To perform a dot product on input vectors, use the Dot Product block.

• If only multiplication of inputs is required, then a numeric parameter value equal to the number of inputs can be supplied instead of "*" characters. This may be used in conjunction with either element-wise or matrix multiplication.
• If a single vector is input and the Multiplication parameter is set to Element-wise, then a single "*" will cause the block to output the scalar product of the vector elements. A single "/" will cause the block to output the inverse of the scalar product of the vector elements.
• If a single matrix is input and the Multiplication parameter is set to Element-wise, then a single "*" or "/" will cause the block to error out. If, however, the Multiplication parameter is set to Matrix, then a single "*" will cause the block to output the matrix unchanged, and a single "/" will cause the block to output the inverse of the matrix.

The Product block first performs the specified multiply or divide operations on the inputs, and then converts the results to the output data type using the specified rounding and overflow modes.

Data Type Support

The Product block accepts real or complex signals of any data type supported by Simulink, except Boolean. The Product block supports 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 Product dialog appears as follows:

Number of inputs

Enter the number of inputs or a combination of "*" and "/" symbols. See Description above for a complete discussion of this parameter.

Multiplication

Specify element-wise or matrix multiplication. See Description above for a complete discussion of this parameter.

Sample time (-1 for inherited)

Specify the time interval between samples. To inherit the sample time, set this parameter to -1. See Specifying Sample Time in the online documentation for more information.

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

Require all inputs to have same data type

Select this parameter to require that all inputs have the same data type.

Output data type mode

Specify the output data type and scaling to be the same as the first input, or inherit the data type and scaling by an internal rule or by backpropagation. You can also choose a built-in data type from the drop-down list. Lastly, if you choose Specify via dialog, the Output data type, Output scaling value, and Lock output scaling against changes by the autoscaling tool parameters become visible.

If you select Inherit via internal rule for this parameter, Simulink chooses a combination of output scaling and data type that requires the smallest amount of memory consistent with accommodating the output range and maintaining the output precision (and avoiding underflow in the case of division operations). If the Device type parameter on the Hardware Implementation pane of the Configuration Parameters dialog is set to custom, Simulink chooses the data type without regard to hardware constraints. Otherwise, Simulink chooses the smallest available hardware data type capable of meeting range, precision, and underflow constraints. For example, if the block multiplies inputs of type int8 and int16 and custom is specified as the device type, the output data type is sfix24. If Unspecified (assume 32-bit generic) is specified, the output data type is int32. If none of the word lengths provided by the target hardware can accommodate the output range, Simulink displays an error message in the Simulation Diagnostics Viewer.

Output data type

Specify any data type, including fixed-point data types. 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.

Lock output scaling against changes by the autoscaling tool

Select to lock scaling of outputs. This parameter is only visible if you select Specify via dialog for the Output data type mode parameter.

Round integer calculations toward

Select the rounding mode for fixed-point operations.

Saturate on integer overflow

Select to have overflows saturate.

Characteristics

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

Prelookup Index Search

Product of Elements

© 1994-2005 The MathWorks, Inc.