While loop in MATLAB: Everything You Need to Know

Introduction

MATLAB is a scientific programming language that is used meticulously by developers for its educational value and relevance. Developed by MathWorks, MATLAB needs pre-licensing before usage for organizations and limited free-usage for students.

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Today, we are talking about the fundamentals of while loop in MATLAB which are condition functions that help in the execution of the statement when the condition satisfies. For a beginner-focused on learning about the basics of MATLAB, today we will entirely concentrate on the working of the while loop. 

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The While Loop in MATLAB

Used in iteration, the while loop is used when there is a need for continuous execution of the statement, as criteria are met. The statements that are executed need to have non-zero elements, and when the condition is false, the loop will stop. 

Syntax of while loop: 

while (condition)

  [perform code]

end

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How to Use MATLAB While Loop

The following flowchart shows how the while loop in MATLAB works. Review the steps elaborating on the working of the while loop in MATLAB:

1. The “condition” will be checked when the loop is initiated. Once the condition becomes true, the code inside of the loop will be executed. If the “condition” is initially not true, the loop is completely skipped over, and the code that follows after the loop is executed immediately.
2. The code in the block is performed when the loop is entered. This block often consists of one or several statements carrying out particular operations or computations.
3. The program then returns to the starting position of the loop and re-evaluates the “condition” after performing the code in the block. If the “condition” remains true, the code in the block will be executed again. Until the condition turns out to be false, this loop is repeated.
4. The program ends the loop and executes the code that comes after it when the condition stands false.

Understanding the syntax and scope: 

• Here, ‘while’ stands as the keyword for the while loop/function.
• The condition statement is similar to a trigger that works only when the case is true.
• For a program that doesn’t satisfy the condition value anytime, the function never executes.
• Here, ‘end’ refers to the end of the program, which is generally handy when conditions aren’t met. 
• If a condition always meets in a program, using the while loop can set off an infinite loop chain entirely. 

Here’s an example: 

x = 20;

while (x<30)

fprintf (‘value of x: %d\n’, a);

x = x+1;

end

Understanding the function:

• First, the variable is defined with a certain value; here, it is 30.
• Second, we place the while loop and with the condition of it running until x is lesser than 30. Which means the loop would have a scope from x=20 to x=29. 
• The ‘fprintf’ function displays the value of x on the screen.
• Then, the next line increases the value of x every time it runs, by 1. 
• Therefore, the loop runs until 29 (i.e., 10 times, starting from 20) and then stops as x=30 isn’t lesser than 30. 

Based on the above explanation, the output of the above program would be: 

value of x: 20

value of x: 21

value of x: 22

value of x: 23

value of x: 24

value of x: 25

value of x: 26

value of x: 27

value of x: 28

value of x: 29

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Things to Remember:

• Non-scalar Expressions: These refer to the executed statements that generate a non-scalar or a combination of true and false cases. In such situations, the entire expression needs to be true for all cases, to get executed as a true statement in a while loop. For example: 

Given matrices A and B

A =                 B =

                    1     0            1     1

                    2     3            3     4

Here, the while (A < B) is true for cases where the corresponding A value is lesser than B, and here, the condition fails when A (1,1) since A1 (1) is not smaller than B1 (1). 

• Partial Evaluation of Expression Arguments: 

In MATLAB, expression generally consists of variables that are joined by relational operators like <, >, =, , ≈, ≤, ≥

A simple statement that combines logical operators into compound statements like 

(count > limit) & ((size – offset)) 0) 

Here, the expression executes only when the entire statement is true and non-zero. 

Sometimes in MATLAB, for a while statement, a logical expression doesn’t get fully evaluated in all its parts. For example: 

while (A & B) = 1;

A = B+1;

printf (‘%A’, B);

end

If A = 0 and B =1, here, the expression doesn’t get executed irrespective of the value of B. Therefore, MATLAB doesn’t consider the need to evaluate B for the ‘&’ operator since they need to be mutually true for the function to progress. 

Similarly in the case of 

while (A|B) = 1;

A = B+1;

printf (‘%A’, B);

end

If A = 1 and B= 0, here, the expression gets executed as soon as A=1, since ‘|’ operator in MATLAB reads the statement true as soon as one variable satisfies the condition. It doesn’t feel the need to evaluate the second variable. 

• You can always end the execution of an infinite loop by pressing Ctrl+C.
• You can have nesting of while statements with each statement followed by the code and its end keyword.

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What is While Loop in MATLAB: Pitfalls and Debugging 

Some of the pitfalls you can have when you are using while loop in MATLAB and the debugging of the errors are as follows:

Infinite Loops

Error: The most prevalent problem with while loops is the possibility of an infinite loop, which occurs when the loop condition never turns into false, and the loop continues to execute endlessly. This may occur if the loop-ending condition has not been correctly specified or if the condition is never arrived at. 

Debug: To resolve this, insert print statements or show values for variables inside the loop to track the loop’s execution and determine why the condition for termination is not getting satisfied. You can additionally set breaks and analyze the code to determine how the loop’s condition will be evaluated.

Improper Loop Termination

Error: Another common error is inappropriately declaring the termination condition, which may result in the loop terminating early or not terminating in any way. Make sure the loop’s ending condition confirms that it correctly matches the condition you would like to test. When applying many different conditions, carefully use logical operators (such as && and ||).

Debug: You may resolve this by printing all the appropriate variables utilized during the termination condition and examining whether or not their values match the intended values. Breakpoints can also be used to proceed across the code and analyze variable values for errors.

Logical Errors

Error: Logical mistakes may occur whenever the loop condition or the conditions inside the loop’s main body have not been correctly constructed. Verify your logical operators and conditional expressions to ensure everything functions as intended. 

Debug: To determine how the conditions have been evaluated and how well they generate the expected outcomes, you may use printing statements or display variable values. Write the necessary conditional expressions by correctly applying MATLAB’s logical operators and functions (such as &&, ||, and is equal).

Using MATLAB Debugging Techniques

MATLAB has a predesigned set of tools that can be used to debug certain errors in the program code: 

1. MATLAB has a number of debugging tools that are designed that can help in finding and fixing errors with while loops. 
2. Breakpoints allow users to terminate the execution of the program at specified lines of code to examine the values of the variables. 
3. Additionally, the MATLAB Editor provides a debugging mode where you may step through each line of code to see how variables change and analyze conditions.
4. MATLAB’s built-in functions, including disp(), fprintf(), and error(), can also be useful for displaying debug statements or error messages so you can monitor progress and highlight particular issues.

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