MATLAB: How to get the matrix to populate with correct values from for loop

Question

Hello. I first create a matrix by using logspace and I convert it to a 50 row and 1 column matrix. I then create a for loop that polpulates column 2 per the number obtained from my for loop, (50 iterations). The values from my column one are used inside the for loop. The first iteration is done perfectly. Values (1,1) was used and populated value (1,2) . When my for loop continues to iteration 2 to 50, the rest of colum 2 is populted by 1's. Can someone please help me understand why it does not do as it first did?

    format long
    h = logspace(-9, -4);
    h = h'
    for j = 1 : 50
        eps = h(j,1)
        for i = 1 : 101
            c = xm;
            xm = (xa + xb) / 2;
            t(i) = abs((xm - c ) / xm);
            if t(i) <= eps
                break
            end
            if t(i) > eps
                if y(xa) < 0 && y(xm) > 0
                    xb = xm;
                end
                if y(xa) > 0 && y(xm) < 0
                    xb = xm;
                end
                if y(xm) < 0 && y(xb) > 0
                    xa = xm;
                end
                if y(xm) > 0 && y(xb) <0
                    xa = xm;
                end
            end
            if i == 100
                break
            end 
            i = i + 1;
       end
        h(j, 2) = (i)
        j = j + 1
    end
    p = h(:,1);
    k = h(:,2);
    semilogx(p,k)

Answer 1

            xm = (xa + xb) / 2;

You do not reset xa and xb to their original values for each j value.