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Math Function - Perform mathematical function

Library

Math Operations

Description

The Math Function block performs numerous common mathematical functions.

You can select one of the following functions from the Function parameter list.

Function	Description	Mathematical Expression	MATLAB Equivalent
exp	Exponential	eu	exp
log	Natural logarithm	ln u	log
10^u	Power of base 10	10u	10.^u (see power)
log10	Common (base 10) logarithm	log u	log10
magnitude^2	Complex modulus	|u|2	(abs(u)).^2 (see abs and power)
square	Power 2	u2	u.^2 (see power)
sqrt	Square root	u0.5	sqrt
1/sqrt	Reciprocal of a square root	u-0.5	—
pow	Power	uv	power
conj	Complex conjugate	ū	conj
reciprocal	Reciprocal	1/u	1./u (see rdivide)
hypot	Square root of sum squares	(u2+v2)0.5	hypot
rem	Remainder after division	—	rem
mod	Modulus after division	—	mod
transpose	Transpose	uT	u.' (see arithmetic operators)
hermitian	Complex conjugate transpose	uH	u' (see arithmetic operators)

The block output is the result of the operation of the function on the input or inputs. The functions support the following types of operations.

Function	Scalar Operations	Element-Wise Vector and Matrix Operations	Vector and Matrix Operations
exp	yes	yes	—
log	yes	yes	—
10^u	yes	yes	—
log10	yes	yes	—
magnitude^2	yes	yes	—
square	yes	yes	—
sqrt	yes	yes	—
1/sqrt	yes	yes	—
pow	yes	yes	—
conj	yes	yes	—
reciprocal	yes	yes	—
hypot	yes, on two inputs	yes, on two inputs (two vectors or two matrices of the same size, a scalar and a vector, or a scalar and a matrix)	—
rem	yes, on two inputs	yes, on two inputs (two vectors or two matrices of the same size, a scalar and a vector, or a scalar and a matrix)	—
mod	yes, on two inputs	yes, on two inputs (two vectors or two matrices of the same size, a scalar and a vector, or a scalar and a matrix)	—
transpose	yes	—	yes
hermitian	yes	—	yes

The name of the function appears on the block. The appropriate number of input ports appears automatically.

Tip   Use the Math Function block instead of the Fcn block when you want vector or matrix output, because the Fcn block produces only scalar output.

Data Type Support

The following table shows the input data types that each function of the block can support.

Function	single	double	boolean	built-in integer	fixed point
exp	yes	yes	—	—	—
log	yes	yes	—	—	—
10^u	yes	yes	—	—	—
log10	yes	yes	—	—	—
magnitude^2	yes	yes	—	yes	yes
square	yes	yes	—	yes	yes
sqrt	yes	yes	—	yes	yes
1/sqrt	yes	yes	—	yes	yes
pow	yes	yes	—	—	—
conj	yes	yes	—	yes	yes
reciprocal	yes	yes	—	yes	yes
hypot	yes	yes	—	—	—
rem	yes	yes	—	yes	—
mod	yes	yes	—	yes	—
transpose	yes	yes	yes	yes	yes
hermitian	yes	yes	—	yes	yes

All supported modes accept both real and complex inputs, except for reciprocal, sqrt, and 1/sqrt, which do not accept complex fixed-point inputs. Also, sqrt and 1/sqrt do not accept fixed-point inputs that are negative or have nontrivial slope and nonzero bias.

The block output is real or complex, depending on what you select for Output signal type. For 1/sqrt, the output is always real and you cannot change the setting for Output signal type.

Parameters and Dialog Box

The Main pane of the Math Function block dialog box appears as follows:

Function

Specify the mathematical function. See Description for more information about the options for this parameter.

Output signal type

Specify the output signal type of the Math Function block as real, complex, or auto.

	Input	Output Signal Type
Function	Signal	Auto	Real	Complex
exp, log, 10u, log10, square, sqrt, pow, reciprocal, conjugate, transpose, hermitian	real complex	real complex	real error	complex complex
magnitude squared	real complex	real real	real real	complex complex
hypot, rem, mod	real complex	real error	real error	complex error
1/sqrt	real complex	real error	Not available	Not available

Sample time (-1 for inherited)

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

The Signal Attributes pane of the Math Function block dialog box appears as follows:

Note   Some parameters on this pane are available only when the function you select in the Function parameter supports fixed-point data types.

Output minimum

Specify the minimum value that the block can output. The default value, [], is equivalent to -Inf. Simulink software uses this value to perform:

• Simulation range checking (see Checking Signal Ranges)

• Automatic scaling of fixed-point data types

Output maximum

Specify the maximum value that the block can output. The default value, [], is equivalent to Inf. Simulink software uses this value to perform:

• Simulation range checking (see Checking 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.

See Specifying Block Output Data Types for more information.

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 Fixed-Point Tool and Fixed-Point Advisor in the Simulink Fixed Point documentation.

Integer rounding mode

Select the rounding mode for fixed-point operations. For more information, see Rounding in the Simulink Fixed Point User's Guide.

Saturate on integer overflow

If selected, fixed-point overflows saturate. Otherwise, overflows wrap.

When you select this check box, saturation applies to every internal operation on the block, not just the output or result. In general, the code generation process can detect when overflow is not possible, in which case, no saturation code is necessary.

The Intermediate Attributes pane of the Math Function block dialog box appears as follows:

Note   The following parameters are available only if you select 1/sqrt for the Function parameter.

Intermediate results data type

Specify the data type for intermediate results. You can set it to:

• Inherit: Inherit via internal rule (default)

• Inherit: Inherit from input

• Inherit: Inherit from output

Tip   Do not select Inherit: Inherit from output under these conditions: You select Newton-Raphson to compute the reciprocal of a square root. The input data type is floating-point. The output data type is fixed-point. Under these conditions, selecting Inherit: Inherit from output yields suboptimal performance and an error results. To avoid this error, convert the input signal from a floating-point to fixed-point data type. For example, insert a Data Type Conversion block in front of the Math Function block to perform the conversion.

Method

Select the method for computing the reciprocal of a square root.

Method	Data Types Supported	When to Use This Method
Newton-Raphson (default)	Floating-point, fixed-point, and built-in integer types	You want a fast, approximate calculation.
Exact	Floating-point If you use a fixed-point or built-in integer type, an upcast to a floating-point type occurs.	You want an exact calculation. Note   The input or output must be floating-point.

Number of iterations

Specify the number of iterations to perform the Newton-Raphson algorithm. The default value is 3.

This parameter is not available when you select Exact for the Method.

Characteristics

Direct Feedthrough	Yes
Sample Time	Specified in the Sample time parameter
Scalar Expansion	Yes, of the input when the function requires two inputs
Dimensionalized	Yes
Multidimensionalized	Yes, for all functions except hermitian and transpose
Zero-Crossing Detection	No

Manual Switch

MATLAB Fcn

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