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Loops: for, while

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In this section, we will explore the use of loops in MATLAB, focusing on the for and while loops. Loops are essential for performing repetitive tasks efficiently. We will cover the syntax, provide practical examples, and include exercises to reinforce the concepts.

  1. Introduction to Loops

Loops allow you to execute a block of code multiple times. MATLAB supports two primary types of loops:

  • for loops
  • while loops

1.1 for Loops

A for loop repeats a group of statements a fixed, predetermined number of times. The syntax is:

for index = start_value:end_value
    % Statements to execute
end

1.2 while Loops

A while loop repeats a group of statements an indefinite number of times as long as a specified condition remains true. The syntax is:

while condition
    % Statements to execute
end

  1. for Loops

2.1 Basic Syntax

The for loop iterates over a sequence of values. Here is a simple example:

for i = 1:5
    disp(['Iteration: ', num2str(i)])
end

Explanation:

  • i = 1:5 creates a vector [1, 2, 3, 4, 5].
  • The loop runs five times, with i taking values from 1 to 5.
  • disp displays the current iteration number.

2.2 Nested for Loops

You can nest for loops to handle multi-dimensional data:

for i = 1:3
    for j = 1:2
        disp(['i = ', num2str(i), ', j = ', num2str(j)])
    end
end

Explanation:

  • The outer loop runs three times.
  • The inner loop runs twice for each iteration of the outer loop.

2.3 Practical Example

Calculate the sum of the first 10 natural numbers:

sum = 0;
for i = 1:10
    sum = sum + i;
end
disp(['Sum of first 10 natural numbers: ', num2str(sum)])

Explanation:

  • Initialize sum to 0.
  • Add each number from 1 to 10 to sum.

  1. while Loops

3.1 Basic Syntax

The while loop continues to execute as long as the condition is true:

i = 1;
while i <= 5
    disp(['Iteration: ', num2str(i)])
    i = i + 1;
end

Explanation:

  • Initialize i to 1.
  • The loop runs while i is less than or equal to 5.
  • Increment i by 1 in each iteration.

3.2 Practical Example

Find the smallest power of 2 greater than 100:

n = 1;
result = 2;
while result <= 100
    result = 2^n;
    n = n + 1;
end
disp(['Smallest power of 2 greater than 100: ', num2str(result)])

Explanation:

  • Initialize n to 1 and result to 2.
  • Continue doubling result until it exceeds 100.

  1. Exercises

Exercise 1: Sum of Even Numbers

Write a for loop to calculate the sum of all even numbers between 1 and 20.

Solution:

sum = 0;
for i = 2:2:20
    sum = sum + i;
end
disp(['Sum of even numbers between 1 and 20: ', num2str(sum)])

Exercise 2: Factorial Calculation

Write a while loop to calculate the factorial of a given number n.

Solution:

n = 5; % Example number
factorial = 1;
i = 1;
while i <= n
    factorial = factorial * i;
    i = i + 1;
end
disp(['Factorial of ', num2str(n), ' is: ', num2str(factorial)])

Exercise 3: Fibonacci Sequence

Write a for loop to generate the first 10 numbers in the Fibonacci sequence.

Solution:

fib = zeros(1, 10);
fib(1) = 1;
fib(2) = 1;
for i = 3:10
    fib(i) = fib(i-1) + fib(i-2);
end
disp('First 10 Fibonacci numbers:')
disp(fib)

  1. Common Mistakes and Tips

Common Mistakes

  • Off-by-one errors: Ensure loop indices are correctly set.
  • Infinite loops: Always update the loop variable in while loops to avoid infinite loops.

Tips

  • Use break to exit a loop early if a condition is met.
  • Use continue to skip the current iteration and proceed to the next one.

Conclusion

In this section, we covered the basics of for and while loops in MATLAB. We explored their syntax, provided practical examples, and included exercises to practice. Understanding loops is crucial for efficient programming and handling repetitive tasks. In the next section, we will delve into functions, their definitions, and scope in MATLAB.

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