Simulink Reference

Fcn

Apply a specified expression to the input

Library

User-Defined Functions

Description

The Fcn block applies the specified C language style expression to its input. The expression can be made up of one or more of these components:

• u -- The input to the block. If u is a vector, u(i) represents the ith element of the vector; u(1) or u alone represents the first element.
• Numeric constants
• Arithmetic operators (+ - * /^)
• Relational operators (== != > < >= <=) -- The expression returns 1 if the relation is true; otherwise, it returns 0.
• Logical operators (&& || !) -- The expression returns 1 if the relation is true; otherwise, it returns 0.
• Parentheses
• Mathematical functions -- abs, acos, asin, atan, atan2, ceil, cos, cosh, exp, fabs, floor, hypot, ln, log, log10, pow, power, rem, sgn, sin, sinh, sqrt, tan, and tanh.
• Workspace variables -- Variable names that are not recognized in the preceding list of items are passed to MATLAB for evaluation. Matrix or vector elements must be specifically referenced (e.g., A(1,1) instead of A for the first element in the matrix).

Note    The Fcn block does not support tunable parameters, i.e., it ignores changes in the values of workspace variables during simulation. The Fcn block also does not support Custom Storage Classes (see the Real-Time Workshop documentation for more information).

The Fcn block observes the following rules of operator precedence:

1. ( )
2. ^
3. + - (unary)
4. !
5. * /
6. + -
7. > < <= >=
8. == !=
9. &&
10. ||

The expression differs from a MATLAB expression in that the expression cannot perform matrix computations. Also, this block does not support the colon operator (:).

Block input can be a scalar or vector. The output is always a scalar. For vector output, consider using the Math Function block. If a block is a vector and the function operates on input elements individually (for example, the sin function), the block operates on only the first vector element.

Note    Simulink does not allow you to change the value of the block's Expression parameter while running a model in accelerated mode (see The Simulink Accelerator). Furthermore, Simulink does not update the value of the Fcn expression to reflect changes in the workspace while running in accelerated mode.

Data Type Support

The Fcn block accepts and outputs signals of type double.

Parameters and Dialog Box

Expression

The C language style expression applied to the input. Expression components are listed above. The expression must be mathematically well formed (i.e., matched parentheses, proper number of function arguments, etc.).

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.

Characteristics

Direct Feedthrough	Yes
Sample Time	Inherited from driving block
Scalar Expansion	No
Dimensionalized	No
Zero Crossing	No

Extract Bits

First-Order Hold

© 1994-2005 The MathWorks, Inc.