Lecture Notes: The NOT Operator in MATLAB

Introduction

• The NOT operator is represented by the tilde ~.
• It is used to invert logical values.
• Logical values include true and false.

Basic Usage

• NOT Operator on Logical Values:
  • ~true → Results in false (0).
  • ~false → Results in true (1).

Applying NOT to Numerical Values

• MATLAB interprets numeric values:
  • 0 is considered as false.
  • Any non-zero value is considered as true.
• Examples:
  • Variable a = 5: ~a results in 0 (since 5 is considered true).
  • Variable b = 0: ~b results in 1 (since 0 is false).
  • Variable c = -3: ~c results in 0 (since any non-zero, e.g., -3, is true).

Logical Questions and Operator Priority

• Sometimes phrasing questions in terms of "not" is easier.
• Example: Instead of asking x <= low, you ask ~(x > low).
• Operator Priority:
  • NOT operator has high priority.
  • It might affect logical expressions if not used carefully.
  • Example: ~x > low is interpreted as 1 > low if x = 0, needing parentheses to correct the precedence.
  • Use parentheses to enforce the desired order of operations.

Practical Tips

• When using logical and relational operators together, use parentheses to prevent mistakes.
• Parentheses help in ensuring the correct evaluation order, especially when unsure of operator precedence.

Additional Example

• Checking if x is outside a range:
  • Original question: Is x between low and high?
  • Use low < x < high.
  • To check if x is NOT between these values, use ~(low < x < high).
  • Since x is between low and high, the expression evaluates to false.

Conclusion

• Operator Priority Reminder: NOT operator has higher precedence over others.
• In the next video, discussion on "and" and "or" operators, focusing on their behavior and precedence.