Find the sum of the non perimeter elements of a matrix using a for loop

I have this matrix

 B=[-3 4 7;9 11 -13;-17 19 -23;-29 31 37;39 41 47]

and I need to find the sum of the non perimeter elements using a for loop. I can find the sum of a single column or row or of the whole matrix, but I don't know how to write a loop to only sum the 3 non perimeter numbers. Any help is appreciated, thank you.

Answer 1

[Image Analyst]

Try it this way:

B=[-3 4 7;9 11 -13;-17 19 -23;-29 31 37;39 41 47]
[rows, columns] = size(B)
theSum = 0;
for col = 2 : columns - 1
  for row = 2 : rows-1
    theSum = theSum + B(row, col);
  end
end
fprintf('The sum = %f\n', theSum);

[Vinny]

Thank you! How about if I wanted it to find the sum of the perimeter elements?

[Image Analyst]

Hopefully you're not just asking me to do all your homework for you. Here is one way:

B=[-3 4 7;9 11 -13;-17 19 -23;-29 31 37;39 41 47]
[rows, columns] = size(B)
theSum = 0;
for col = 1 : columns
  for row = 1 : rows
    if row == 1 || row == rows || col == 1 || col == columns
      % It's on the perimeter of the array.
      theSum = theSum + B(row, col)
    end
  end
end
fprintf('The sum = %f\n', theSum);

Answer 2

[Azzi Abdelmalek]

A=B
A(:,[1 end])=0
A([1 end],:)=0
out=sum(A(:))

Answer 3

[Ibrahim Abouemira]

Hello,

Here's a function that performs your required task.

https://www.mathworks.com/matlabcentral/fileexchange/71595-sum-of-values-on-the-perimeter-of-a-matrix