numerictype Object Properties

Data Type and Scaling Properties

All properties of a numerictype object are writable. However, the numerictype properties of a fi object become read only after the fi object has been created. Any numerictype properties of a fi object that are unspecified at the time of fi object creation are automatically set to their default values. The properties of a numerictype object are:

Property	Description	Valid Values
Bias	Bias associated with the object. Along with the slope, the bias forms the scaling of a fixed-point number.	Any floating-point number
DataType	Data type category	Fixed (default) — Fixed-point or integer data type boolean — Built-in MATLAB® boolean data type double — Built-in MATLAB double data type ScaledDouble — Scaled double data type single — Built-in MATLAB single data type
DataTypeMode	Data type and scaling associated with the object	Fixed-point: binary point scaling (default) — Fixed-point data type and scaling defined by the word length and fraction length Boolean — Built-in boolean Double — Built-in double Fixed-point: slope and bias scaling — Fixed-point data type and scaling defined by the slope and bias Fixed-point: unspecified scaling — Fixed-point data type with unspecified scaling Scaled double: binary point scaling — Double data type with fixed-point word length and fraction length information retained Scaled double: slope and bias scaling — Double data type with fixed-point slope and bias information retained Scaled double: unspecified scaling — Double data type with unspecified fixed-point scaling Single — Built-in single
FixedExponent	Fixed-point exponent associated with the object	Any integer Note The FixedExponent property is the negative of the FractionLength. Changing one property changes the other.
FractionLength	Fraction length of the stored integer value, in bits	Best precision fraction length based on value of the object and the word length (default) Any integer Note The FractionLength property is the negative of the FixedExponent. Changing one property changes the other.
Scaling	Scaling mode of the object	BinaryPoint (default) — Scaling for the fi object is defined by the fraction length. SlopeBias — Scaling for the fi object is defined by the slope and bias. Unspecified — A temporary setting that is only allowed at fi object creation, to allow for the automatic assignment of a binary point best-precision scaling.
Signed	Whether the object is signed Note Although the Signed property is still supported, the Signedness property always appears in the numerictype object display. If you choose to change or set the signedness of your numerictype objects using the Signed property, MATLAB updates the corresponding value of the Signedness property.	true (default) — signed false — unsigned 1 — signed 0 — unsigned [] — auto
Signedness	Whether the object is signed, unsigned, or has an unspecified sign	Signed (default) Unsigned Auto — unspecified sign
Slope	Slope associated with the object Along with the bias, the slope forms the scaling of a fixed-point number.	Any finite floating-point number greater than zero Note $$slope=slopeadjustmentfactor\times 2^{fixedexponent}$$ Changing one of these properties changes the other.
SlopeAdjustmentFactor	Slope adjustment associated with the object The slope adjustment is equivalent to the fractional slope of a fixed-point number.	Any number greater than or equal to 1 and less than 2 Note $$slope=slopeadjustmentfactor\times 2^{fixedexponent}$$ Changing one of these properties changes the other.
WordLength	Word length of the stored integer value, in bits	16 (default) Any positive integer if Signedness is Unsigned or unspecified Any integer greater than one if Signedness is set to Signed

These properties are described in detail in the fi Object Properties. To learn how to specify properties for numerictype objects in Fixed-Point Designer™ software, refer to Set numerictype Object Properties.

How Properties are Related

Properties that affect the slope

The Slope field of the numerictype object is related to the SlopeAdjustmentFactor and FixedExponent properties by

$$slope=slopeadjustmentfactor\times 2^{fixedexponent}$$

The FixedExponent and FractionLength properties are related by

$$fixedexponent=-fractionlength$$

If you set the SlopeAdjustmentFactor, FixedExponent, or FractionLength property, the Slope field is modified.

Stored integer value and real world value

In binary point scaling the numerictype StoredIntegerValue and RealWorldValue properties are related according to

$$real\text{-}worldvalue=storedintegervalue\times 2^{-fractionlength}$$

In [Slope Bias] scaling the RealWorldValue can be represented by

$$\begin{array}{l}real\text{-}worldvalue=\\ storedintegervalue\times (slopeadjustmentfactor\times 2^{fixedexponent})+bias\end{array}$$

which is equivalent to

$$real\text{-}worldvalue=(slope\times storedinteger)+bias$$

If any of these properties are updated, the others are modified accordingly.

Set numerictype Object Properties

Setting numerictype Properties at Object Creation

You can set properties of numerictype objects at the time of object creation by including properties after the arguments of the numerictype constructor function.

For example, to set the word length to 32 bits and the fraction length to 30 bits,

T = numerictype('WordLength',32,'FractionLength',30)

T =
 

          DataTypeMode: Fixed-point: binary point scaling
            Signedness: Signed
            WordLength: 32
        FractionLength: 30

In addition to creating a numerictype object at the command line, you can also set numerictype properties using the Insert numerictype Constructor dialog box. For an example of this approach, see Example: Build numerictype Object Constructors in a GUI.

Use Direct Property Referencing with numerictype Objects

You can reference directly into a property for setting or retrieving numerictype object property values using MATLAB structure-like referencing. You do this by using a period to index into a property by name.

For example, to get the word length of T,

T.WordLength

ans =

32

To set the fraction length of T,

T.FractionLength = 31

T =
 

          DataTypeMode: Fixed-point: binary point scaling
            Signedness: Signed
            WordLength: 32
        FractionLength: 31