Finding the norm of a matrix using for-loops and conditional statements

Alright, so I'm having a bit of trouble with an example for MATLAB. I'm trying to find the conditional number of any square matrix, which normally isn't too difficult. However, instead of using the norm function to find the norm of the matrix, I am to use loops and conditional statements. I'm not completely sure where to start.

I know how to find the norm on paper - I take the absolute value of each number of the matrix, then add up the columns. The largest number, then, is the norm of the matrix. How might I translate that over into MATLAB?

EDIT: This is how what I've gotten thus far. The sums make sense, but I don't know how to edit it so that it'll work for any square matrix.

A= [2 3 4; 4 7 6; -11 85 9;];
invA= inv(A);
mn=size(A);
n=length(A);

for i=1:1:n-2
    for j=1:1:n-2
        sum_1=abs(A(i,1)) + abs(A((i+1),1) + abs(A((i+2),1)))
        sum_2=abs(A(i,2)) + abs(A((i+1),2)) + abs(A((i+2),2))
        sum_3=abs(A(i,3)) + abs(A((i+1),3)) + abs(A((i+2),3))
    end
end

[Matt J]

Why not just use cond()

[Chris]

I'm supposed to use loops and conditional statements - I can't use max/cond/sum/similar commands.

[Matt J]

I know how to find the norm on paper - I take the absolute value of each number of the matrix, then add up the columns.

That is the L1 norm, not the more standard L2 norm.

Answer 1

[Matt J]

Hint:

     B=abs(A);

     accum=0; 
     for i=1:size(B,1)

      accum=accum+B(i,:);

     end

[Chris]

That makes sense, I appreciate it. What does the : signify in the B(i,:); portion?

[Chris]

Nevermind, figured what the : was.

Answer 2

[Chris]

I greatly appreciate that little hint you gave me - that little nudge in the right direction was just what I needed.