Check logical expressions in If blocks

Check ID: mathworks.maab.na_0003

Guideline: na_0003: Usage of If blocks

• MAB v5.0

• JMAAB v5.1

• JMAAB v6.0

Description

Check If blocks for inappropriate construct of primary expressions in a logical expression.

Identifies instances in an If block where primary expressions are complex.

Primary expressions are defined as:

• An input

• A constant

• A constant parameter

• A parenthesized expression containing no operators other than zero or <, >, >=, <=, ==, ~=, |, &, and ~

Examples of primary expressions include:

• u1

• 5

• K

• (u1 > 0)

• (u1 <= G)

• (u1 > U2)

• (~u1)

Examples of acceptable logical expressions exceptions include:

• u1 | u2

• ((u1 > 0) & (u1 < 20)

• (u1 > 0) & (u2 < u3)

• (u1 > 0) & (~u2)

This table provides examples of unacceptable logical expressions.

Primary Expression	Reasoning
u1 & u2 | u3	Too many primary expressions.
u1 & (u2 | u3)	Unacceptable operator within primary expression.
(u1 > 0) & (u1 < 20) & (u2 > 5)	Too many primary expressions that are not inputs.
(u1 > 0) & ((2* u2) > 6)	Unacceptable operator within primary expression.

Exception

A logical expression can contain more than two primary expressions when both these conditions are met:

• The primary expressions are all inputs.

• Only one type of logical operator is present.

Examples of acceptable exceptions include:

• u1 | u2 | u3 | u4 | u5

• u1 & u2 & u3 & u4

Simple "If" Expressions

In the literal interpretation of guideline na_0003, expression u1 < u2 is a violation. However, the expression follows the commonly used "If" expression template (<Primary Expression><Operator><Primary Expression>). So, when logical operators are not used and only one relational operator is present, the expression satisfies guideline na_0003 and u1 < u2 is NOT a violation.

This check requires a Simulink^® Check™ license.

Check Parameterization

This check does not include sub-checks because the MAB modeling guideline only provides one sub ID.

For reference, the MAB guideline sub ID(s) that are recommended for use by the NA-MAAB and JMAAB modeling standards organizations are:

• NA-MAAB — No recommendations

• JMAAB — a

Results and Recommended Actions

Condition	Recommended Action
Logical expression contains more than two primary expressions that consist of a constant, constant parameter, and input.	Consider one of the following: Make primary expressions an input and either: Use parenthesized expressions with one relational operator type Construct a simple "If" express using template <Primary Expression><Logical Operator><Primary Expression> Reduce the number of primary expressions to two or less. Construct the logical expression using logical blocks other than the If block.
Logical expression contains more than two parenthesized expressions that use multiple relational operators	Consider one of the following: Use only one type of relational operator. Acceptable logical operators include <, >, >=, <=, ==, ~=, |, &, and ~. The primary expression must consist of inputs only. Reduce the number of parenthesized expressions to two or less. Construct the logical expression using logical blocks other than the If block.
Parenthesized expression includes a relational operator other than zero or <, >, >=, <=, ==, ~=, |, &, or ~.	Consider one of the following: Use relational operator <, >, >=, <=, ==, ~=, |, &, or ~ within the parenthesized expression. Construct the logical expression using logical blocks other than the If block.

Capabilities and Limitations

• Does not flag logical expressions that use only one of these relative operators <, >, >=, <=, ==, ~=, |, &, and ~

• Runs on library models.

• Analyzes content of library-linked blocks. By default, the input parameter Follow links is set to on.

• Analyzes content in masked subsystems. By default, the input parameter Look under masks is set to graphical.