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# Dot Product

Generate dot product of two vectors

Math Operations

## Description

The Dot Product block generates the dot product of the vectors at its inputs. The scalar output, y, is equal to the MATLAB® operation

```y = sum(conj(u1) .* u2 )
```

where u1 and u2 represent the vectors at the block's top and bottom inputs, respectively. (See How to Rotate a Block in the Simulink® documentation for a description of the port order for various block orientations.) The inputs can be vectors, column vectors (single-column matrices), or scalars. If both inputs are vectors or column vectors, they must be the same length. If u1 and u2 are both column vectors, the block outputs the equivalent of the MATLAB expression u1'*u2.

The elements of the input vectors can be real- or complex-valued signals. The signal type (complex or real) of the output depends on the signal types of the inputs.

Input 1Input 2Output

real

real

real

real

complex

complex

complex

real

complex

complex

complex

complex

To perform element-by-element multiplication without summing, use the Product block.

## Data Type Support

The Dot Product block accepts and outputs signals of any numeric data type that Simulink supports, including fixed-point data types.

## Parameters and Dialog Box

The Main pane of the Dot Product block dialog box appears as follows:

The Signal Attributes pane of the Dot Product block dialog box appears as follows:

Sample time (-1 for inherited)

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

Require all inputs to have same data type

Select to require all inputs to have the same data type.

Output minimum

Specify the minimum value that the block should output. The default value is [] (unspecified). Simulink software uses this value to perform:

• Simulation range checking (see Signal Ranges)

• Automatic scaling of fixed-point data types

Output maximum

Specify the maximum value that the block should output. The default value is [] (unspecified). Simulink software uses this value to perform:

• Simulation range checking (see Signal Ranges)

• Automatic scaling of fixed-point data types

Output data type

Specify the output data type. You can set it to:

• A rule that inherits a data type, for example, Inherit: Inherit via back propagation

• The name of a built-in data type, for example, single

• The name of a data type object, for example, a Simulink.NumericType object

• An expression that evaluates to a data type, for example, fixdt(1,16,0)

Click the Show data type assistant button to display the Data Type Assistant, which helps you set the Output data type parameter.

Lock output data type setting against changes by the fixed-point tools

Select to lock the output data type setting of this block against changes by the Fixed-Point Tool and the Fixed-Point Advisor. For more information, see Use Lock Output Data Type Setting.

Integer rounding mode

Specify the rounding mode for fixed-point operations. For more information, see Rounding. in the Fixed-Point Designer™ documentation.

Saturate on integer overflow
ActionReasons for Taking This ActionWhat Happens for OverflowsExample

Select this check box.

Your model has possible overflow, and you want explicit saturation protection in the generated code.

Overflows saturate to either the minimum or maximum value that the data type can represent.

The maximum value that the int8 (signed, 8-bit integer) data type can represent is 127. Any block operation result greater than this maximum value causes overflow of the 8-bit integer. With the check box selected, the block output saturates at 127. Similarly, the block output saturates at a minimum output value of -128.

Do not select this check box.

You want to optimize efficiency of your generated code.

You want to avoid overspecifying how a block handles out-of-range signals. For more information, see Checking for Signal Range Errors.

Overflows wrap to the appropriate value that is representable by the data type.

The maximum value that the int8 (signed, 8-bit integer) data type can represent is 127. Any block operation result greater than this maximum value causes overflow of the 8-bit integer. With the check box cleared, the software interprets the overflow-causing value as int8, which can produce an unintended result. For example, a block result of 130 (binary 1000 0010) expressed as int8, is -126.

When you select this check box, saturation applies to every internal operation on the block, not just the output or result. Usually, the code generation process can detect when overflow is not possible. In this case, the code generator does not produce saturation code.

## Characteristics

 Direct Feedthrough Yes Sample Time Specified in the Sample time parameter Scalar Expansion No States 0 Dimensionalized Yes Zero-Crossing Detection No