The provided MATLAB function `threeSevens` checks if the input array...

The provided MATLAB function threeSevens checks if the input array x contains exactly three occurrences of the number 7. Here's what each line of the code does:

1. count == sum(x==7);
   This line has a mistake. Instead of assigning the result of the comparison to count, it incorrectly uses the equality operator ==.
   The corrected version should instead use a single equals sign =:
   count = sum(x == 7);.
   Here is the intent of the corrected line: it computes how many times the number 7 appears in the array x. The expression (x == 7) creates a logical array of the same size as x, with 1 (true) where the elements of x are 7, and 0 (false) otherwise. The sum function then adds up the 1s, resulting in the total number of 7s.

2. if count == 3
   This checks if the variable count (number of 7s in x) is equal to 3.

3. b = true;
   If the condition is true (the input x contains exactly three 7s), the output b is set to true.

4. else b = false;
   If the condition is false (the input x does not contain exactly three 7s), the output b is set to false.

5. end
   Ends the if-else block.

6. Overall, the function returns the logical value b, which is true if x contains exactly three 7s, and false otherwise.

Corrected Code:

function b = threeSevens(x)
count = sum(x == 7); % Corrected assignment operator
if count == 3 
    b = true; 
else 
    b = false; 
end
end

Example Usage:

threeSevens([1, 7, 2, 7, 3, 7])   % Returns true (exactly 3 sevens)
threeSevens([1, 7, 2, 7])         % Returns false (only 2 sevens)
threeSevens([7, 7, 7, 7])         % Returns false (4 sevens)