Weighted Sample Time Math

Support calculations involving sample time

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Libraries:
Simulink / Math Operations

Description

The Weighted Sample Time block outputs a weighted sample time, weighted sample rate, or mathematically adjusted weighted sample time, depending on settings of the Operation and Weight value parameters and the execution context of the function outputs.

You specify the block operation by using the Operation parameter.

The sample time used to derive the output depends on whether the block is used within a periodic or aperiodic (or triggered) execution context. For a periodic execution context, the block uses the sample time of the model. For an aperiodic or triggered execution context, the block uses the sample time of the discrete signal.

Use the Weight value parameter to specify the sample time weight factor. If the weight value, w, is 1, that value does not appear in the equation on the block icon.

Tip

You can use the Weighted Sample Time and Weighted Sample Time Math blocks to extract the sample time from a Simulink^® signal. Set the Operation parameter to Ts Only and the Weight value parameter to 1.0. With this configuration, the block outputs the sample time of the input signal.

The block computes its output by using the precedence rules for MATLAB^® operators. For example, if the Operation parameter is set to +, the block calculates the output by using this expression:

u + (Ts * w)

If the Operation parameter is set to /, the block calculates the output by using this expression:

(u / Ts) / w)

For more information, see Operator Precedence.

Examples

Sample Time Math Operations Using the Weighted Sample Time Math Block

This example shows how to add the sample time value to a signal using the Weighted Sample Time Math block.

Using the Weighted Sample Time block, you can see the sample time of this model is 0.2. When you set the Operation parameter to + and the Weight value to 1 on the Weighted Sample Time Math block, the block adds the sample time value of 0.2 to the input signal. When you set the Weight value to 3 in the Weighted Sample Time Math1 block, the block adds Ts*3 to the input signal, thus increasing each value by 0.6.

Ports

Input

Port_1 — Input signal

scalar | vector | matrix

Specify input signal as a scalar, vector, or matrix.

Data Types: single | double | int8 | int16 | int32 | int64 | uint8 | uint16 | uint32 | uint64 | Boolean | fixed point

Output

Port_1 — Output signal

scalar | vector | matrix

Depending on settings of the Operation and Weight value parameters and the execution context of the function that contains the block, the block outputs a weighted sample time, weighted sample rate, or mathematically adjusted weighted sample time.

• Weighted sample time –- When used in a periodic function, the weighted sample time is the sample time of an input signal times the value specified for the Weight value parameter (Ts * w). When used in an aperiodic or triggered function, the weighted sample time is the elapsed time since the last execution times the weight value.

• Weighted sample rate –- When used in a periodic function, the weighted sample rate is the reciprocal of the weighted sample time (1/(Ts * w)). The weighted sample rate is not relevant when the block is used in an aperiodic function.

• Mathematically adjusted weighted sample time –- The block adds the value of an input signal u to, subtracts u from, or multiplies or divides u by a weighted sample time.

The sample time used to derive the output and the data type of the output depend on whether the block is used within a periodic or aperiodic (or triggered) execution context.

Execution Context of Block	Sample Time Used to Derive Output	Data Type of Output Signal
Periodic	Sample time of the model	Sign is the same sign as the value of the input signal. Word length is the larger value of the input signal word length or half of a long long. Scaling is best precision scaling of the weighted sample time.
Aperiodic or triggered	Elapsed time since the last execution	Data type is unsigned. Word length is large enough to account for the setting of model configuration parameter Application lifespan. Scaling is best precision scaling of the setting of model configuration parameter Clock resolution.

Data Types: single | double | int8 | int16 | int32 | int64 | uint8 | uint16 | uint32 | uint64 | Boolean | fixed point

Parameters

Main

Operation — Math operation

+ (default) | - | * | / | Ts Only | 1/Ts Only

Specify the operation to use for adjusting the input signal. For example, if you specify the + operation, the block adds the weighted sample time to the value of the input signal. The value 1/Ts Only is not relevant when you use the block in an aperiodic function.

Programmatic Use

Block Parameter: TsampMathOp

Type: character vector

Values: '+' | '-' | '*' | '/' | 'Ts Only' | '1/Ts Only'

Default: '+'

Weight value — Weight for sample time

1.0 (default) | real-valued scalar

Enter the weight for the sample time as a real-valued scalar. The block multiplies the sample time of the input signal by the value that you specify. For example, if you use the block in a periodic function of a model that has a sample time of 0.2 and you specify a weight value of 3, the weighted sample time is 0.6.

Programmatic Use

Block Parameter: weightValue

Type: character vector

Values: real-valued scalar

Default: 1.0

Implement using — Method for adjusting sample time

Online Calculations (default) | Offline Scaling Adjustment

Select whether to adjust the sample time by applying online calculations or by applying offline scaling.

Result of Ts * w	Output Data Type of Two Modes	Block Execution
Power of 2 (positive or negative) or an integer value	The same when Output data type is set to Inherit: Inherit via internal rule	Equally efficient in both modes
Not a power of 2 and not an integer value	Different	More efficient for the offline scaling mode

Note

When the Implement using parameter is not enabled, operations default to online calculations.

Dependencies

To enable this parameter, set Operation to * or /.

Programmatic Use

Block Parameter: TsampMathImp

Type: character vector

Values: 'Online Calculations' | 'Offline Scaling Adjustment'

Default: 'Online Calculations'

Signal Attributes

Output data type — Data type of output signal

Inherit: Inherit via internal rule (default) | Inherit: Inherit via back propagation | double | single | int8 | uint8 | int16 | uint16 | int32 | uint32 | int64 | uint64 | fixdt(1,16,0) | fixdt(1,16,20,0) | <data type expression>

Specify the data type for the block output signal.

Programmatic Use

Block Parameter: OutDataTypeStr

Type: character vector

Values: 'Inherit: Inherit via internal rule' | 'Inherit: Inherit via back propagation' | double | single | int8 | uint8 | int16 | uint16 | int32 | uint32 | int64 | uint64 | fixdt(1,16,0) | fixdt(1,16,20,0) | '<data type expression>'

Default: 'Inherit: Inherit via internal rule'

Integer rounding mode — Rounding mode for fixed-point operations

Floor (default) | Ceiling | Convergent | Nearest | Round | Simplest | Zero

Specify the rounding mode for fixed-point operations. For more information, see Rounding Modes (Fixed-Point Designer).

Block parameters round to the nearest representable value. To control the rounding of a block parameter, enter an expression by using a MATLAB rounding function in the mask field.

Dependencies

To enable this parameter, set the Operation parameter to +, -, *, or /. If you set the Operation to * or /, you must also set the Implement using parameter to Online Calculations.

Programmatic Use

Block Parameter: RndMeth

Type: character vector

Values: 'Ceiling' | 'Convergent' | 'Floor' | 'Nearest' | 'Round' | 'Simplest' | 'Zero'

Default: 'Floor'

Saturate on integer overflow — Method of overflow action

off (default) | on

Specify whether integer overflows saturate or wrap.

Goal	Action	Overflow Behavior	Example
Model has possible overflow conditions and you want explicit saturation protection in the generated code.	Select check box (on).	Saturate to 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. A block operation result greater than this maximum value causes overflow of the 8-bit integer. When you select this parameter, the block output saturates at 127. Similarly, the block output saturates at a minimum output value of -128.
You want to optimize generated code. You want to avoid overspecifying how a block handles out-of-range signals. For more information, see Troubleshoot Signal Range Errors.	Clear check box (off).	Wrap overflows 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. A block operation result greater than this maximum value causes overflow of the 8-bit integer. When you clear this parameter, 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 Saturate on integer overflow, saturation applies to every internal operation on the block, not just the output, or result. When the code generator detects that overflow is not possible, it does not produce saturation code.

Dependencies

To enable this parameter, set the Operation parameter to +, -, *, or /. If you set Operation to * or /, you must also set the Implement using parameter to Online Calculations.

Programmatic Use

Block Parameter: SaturateOnIntegerOverflow

Type: character vector

Values: 'off' | 'on'

Default: 'off'

Mode — Data type mode

Inherit (default) | Built in | Fixed point | Expression

Select how you would like to specify the data type properties of the Output data type. You can choose:

• Inherit — Specify a rule for inheriting a data type, for example, Inherit: Same as input.

• Built in— Specify a built-in data type, for example, double.

• Fixed point — Specify the fixed-point attributes of the data type.

• Expression — Specify an expression that evaluates to a valid data type, for example, fixdt(1,16).

For more information, see Specify Data Types Using Data Type Assistant.

Signedness — Signedness of fixed-point data

Signed (default) | Unsigned

Specify whether the fixed-point data is signed or unsigned. Signed data can represent positive and negative values, but Unsigned data represents positive values only. For more information, see Specify Data Types Using Data Type Assistant.

Scaling — Method for scaling fixed-point data

Best precision (default) | Binary point

Specify the method for scaling your fixed-point data to avoid overflow conditions and minimize quantization errors. For more information, see Specify Data Types Using Data Type Assistant.

Dependencies

To enable this parameter, set Mode to Fixed point

Word length — Bit size of word that holds quantized integer

16 (default) | integer from 2 to 128

Specify the bit size of the word that holds the quantized integer as a positive integer from 2 to 128. For more information, see Specify Data Types Using Data Type Assistant.

Dependencies

To enable this parameter, set Mode to Fixed point.

Fraction length — Fraction length for fixed-point data type

0 (default) | integer scalar

Specify the fraction length of the fixed-point data type as a positive or negative integer scalar.

Dependencies

To enable this parameter, set Mode to Fixed point and Scaling to Binary point.

Slope — Specify slope for the fixed-point data type

2^0 (default) | positive, real-valued scalar

Specify slope for the fixed-point data type. For more information, see Specifying a Fixed-Point Data Type.

Dependencies

To enable this parameter, set Scaling to Slope and bias.

Bias — Specify bias for the fixed-point data type

0 (default) | real-valued scalar

Specify bias for the fixed-point data type as any real number. For more information, see Specifying a Fixed-Point Data Type.

Dependencies

To enable this parameter, set Scaling to Slope and bias.

Data type override — Data type override mode

Inherit (default) | Off

Select the data type override mode for this signal. You can select:

• Inherit — Inherits the data type override setting specified for the model.

• Off — Ignores the data type override setting specified for the model and uses the fixed-point data type you specify.

Dependencies

To enable this parameter, set Mode to Built in or Fixed point. For more information, see Specify Data Types Using Data Type Assistant.

Block Characteristics

Data Types	Boolean | double | fixed point | integer | single
Direct Feedthrough	yes
Multidimensional Signals	no
Variable-Size Signals	no
Zero-Crossing Detection	no

Extended Capabilities

C/C++ Code Generation
Generate C and C++ code using Simulink® Coder™.

Fixed-Point Conversion
Design and simulate fixed-point systems using Fixed-Point Designer™.

Version History

Introduced before R2006a

R2023b: Weighted Sample Time Math Block Update

The Weighted Sample Time Math block now supports:

• Additional output types

  • double

  • single

  • int8

  • uint8

  • int16

  • uint16

  • int32

  • uint32

  • int64

  • uint64

  • fixdt(1,16,0)

  • fixdt(1,16,20,0)

• Fixed point as a new option to the Mode parameter, which enables the fixed-point parameters:

  • Signedness

  • Scaling

  • Word length

  • Slope

  • Bias

  • Data type override