How to find the input value when outputting the maximum value

    [mi] = [dab,dac,dad,dbc,dbd,dcd];
    length = max(mi);

The coordinates of the four points A, B, C, and D are known. I have calculated the distance between the two points through pdist2(). I used max() to get the maximum value of these distances. My current requirement is to convert the maximum The two points are connected by a plot() line, so how can I know the coordinates of the two points of the maximum value?

Answer 1

[Walter Roberson]

[max_length, maxidx] = max(mi);
switch maxidx
    case 1
        coords = {A, B};
    case 2
        coords = {A, C};
    case 3
        coords = {A, D};
    case 4
        coords = {B, C};
    case 5
        coords = {B, D};
    case 6
        coords = {C, D};
    otherwise
        error('strange maximum index!')
end

... It would have been easier to work with the array returned by pdist2() directly.

all_coords = {A, B, C, D};
[max_length, maxidx] = max( reshape(triu(Distance_Matrix), [], 1 );
[R,C] = ind2sub( size(Distance_Matrix), maxidx );
coords = {all_coords{R}, all_coords{C}};

[文辉 沈]

Actually, my problem is a bit complicated, but I've solved it for the time being (it's repetitive work though)

Because the abscissa and ordinate of the four points of abc are changing, we have to use such a cumbersome method. Maybe, do you have a script that can be simplified?

    if rank(find(bw(1,:))) ~= 0 && rank(find(bw(:,1))) ~= 0
        xa = find(bw(1,:), 1, 'first');
        xb = find(bw(1,:), 1, 'last');
        xc = find(bw(:,1), 1, 'first');
        xd = find(bw(:,1), 1, 'last');
        dab = pdist2([xa, 1],[xb, 1]);
        dac = pdist2([xa, 1],[1, xc]);
        dad = pdist2([xa, 1],[1, xd]);
        dbc = pdist2([xb, 1],[1, xc]);
        dbd = pdist2([xb, 1],[1, xd]);
        dcd = pdist2([1, xc],[1, xd]);
        [mi] = [dab,dac,dad,dbc,dbd,dcd];
        [length, maxidx] = max(mi);
        switch maxidx
            case 1
                coord1 = [xa, 1];
                coord2 = [xb, 1];
            case 2
                coord1 = [xa, 1];
                coord2 = [1, xc];
            case 3
                coord1 = [xa, 1];
                coord2 = [1, xd];
            case 4
                coord1 = [xb, 1];
                coord2 = [1, xc];
            case 5
                coord1 = [xb, 1];
                coord2 = [1, xd];
            case 6
                coord1 = [1, xc];
                coord2 = [1, xd];
            otherwise
                error('strange maximum index!')
        end
    elseif rank(find(bw(1,:))) ~= 0 && rank(find(bw(end,:))) ~= 0
        xa = find(bw(1,:), 1, 'first');
        xb = find(bw(1,:), 1, 'last');
        xc = find(bw(end,:), 1, 'first');
        xd = find(bw(end,:), 1, 'last');
        dab = pdist2([xa, 1],[xb, 1]);
        dac = pdist2([xa, 1],[xc, r]);
        dad = pdist2([xa, 1],[xd, r]);
        dbc = pdist2([xb, 1],[xc, r]);
        dbd = pdist2([xb, 1],[xd, r]);
        dcd = pdist2([xc, r],[xd, r]);
        [mi] = [dab,dac,dad,dbc,dbd,dcd];
        [length, maxidx] = max(mi);
        switch maxidx
            case 1
                coord1 = [xa, 1];
                coord2 = [xb, 1];
            case 2
                coord1 = [xa, 1];
                coord2 = [xc, r];
            case 3
                coord1 = [xa, 1];
                coord2 = [xd, r];
            case 4
                coord1 = [xb, 1];
                coord2 = [xc, r];
            case 5
                coord1 = [xb, 1];
                coord2 = [xd, r];
            case 6
                coord1 = [xc, r];
                coord2 = [xd, r];
            otherwise
                error('strange maximum index!')
        end
    elseif rank(find(bw(1,:))) ~= 0 && rank(find(bw(:,end))) ~= 0
        xa = find(bw(1,:), 1, 'first');
        xb = find(bw(1,:), 1, 'last');
        xc = find(bw(:,end), 1, 'first');
        xd = find(bw(:,end), 1, 'last');
        dab = pdist2([xa, 1],[xb, 1]);
        dac = pdist2([xa, 1],[c, xc]);
        dad = pdist2([xa, 1],[c, xd]);
        dbc = pdist2([xb, 1],[c, xc]);
        dbd = pdist2([xb, 1],[c, xd]);
        dcd = pdist2([c, xc],[c, xd]);
        [mi] = [dab,dac,dad,dbc,dbd,dcd];
        [length, maxidx] = max(mi);
        switch maxidx
            case 1
                coord1 = [xa, 1];
                coord2 = [xb, 1];
            case 2
                coord1 = [xa, 1];
                coord2 = [c, xc];
            case 3
                coord1 = [xa, 1];
                coord2 = [c, xd];
            case 4
                coord1 = [xb, 1];
                coord2 = [c, xc];
            case 5
                coord1 = [xb, 1];
                coord2 = [c, xd];
            case 6
                coord1 = [c, xc];
                coord2 = [c, xd];
            otherwise
                error('strange maximum index!')
        end
    elseif rank(find(bw(:,1))) ~= 0 && rank(find(bw(end,:))) ~= 0
        xa = find(bw(:,1), 1, 'first');
        xb = find(bw(:,1), 1, 'last');
        xc = find(bw(end,:), 1, 'first');
        xd = find(bw(end,:), 1, 'last');
        dab = pdist2([1, xa],[1, xb]);
        dac = pdist2([1, xa],[xc, r]);
        dad = pdist2([1, xa],[xd, r]);
        dbc = pdist2([1, xb],[xc, r]);
        dbd = pdist2([1, xb],[xd, r]);
        dcd = pdist2([xc, r],[xd, r]);
        [mi] = [dab,dac,dad,dbc,dbd,dcd];
        [length, maxidx] = max(mi);
        switch maxidx
            case 1
                coord1 = [1, xa];
                coord2 = [1, xb];
            case 2
                coord1 = [1, xa];
                coord2 = [xc, r];
            case 3
                coord1 = [1, xa];
                coord2 = [xd, r];
            case 4
                coord1 = [1, xb];
                coord2 = [xc, r];
            case 5
                coord1 = [1, xb];
                coord2 = [xd, r];
            case 6
                coord1 = [xc, r];
                coord2 = [xd, r];
            otherwise
                error('strange maximum index!')
        end
    elseif rank(find(bw(:,1))) ~= 0 && rank(find(bw(:,end))) ~= 0
        xa = find(bw(:,1), 1, 'first');
        xb = find(bw(:,1), 1, 'last');
        xc = find(bw(:,end), 1, 'first');
        xd = find(bw(:,end), 1, 'last');
        dab = pdist2([1, xa],[1, xb]);
        dac = pdist2([1, xa],[c, xc]);
        dad = pdist2([1, xa],[c, xd]);
        dbc = pdist2([1, xb],[c, xc]);
        dbd = pdist2([1, xb],[c, xd]);
        dcd = pdist2([c, xc],[c, xd]);
        [mi] = [dab,dac,dad,dbc,dbd,dcd];
        [length, maxidx] = max(mi);
        switch maxidx
            case 1
                coord1 = [1, xa];
                coord2 = [1, xb];
            case 2
                coord1 = [1, xa];
                coord2 = [c, xc];
            case 3
                coord1 = [1, xa];
                coord2 = [c, xd];
            case 4
                coord1 = [1, xb];
                coord2 = [c, xc];
            case 5
                coord1 = [1, xb];
                coord2 = [c, xd];
            case 6
                coord1 = [c, xc];
                coord2 = [c, xd];
            otherwise
                error('strange maximum index!')
        end
    elseif rank(find(bw(end,:))) ~= 0 && rank(find(bw(:,end))) ~= 0
        xa = find(bw(end,:), 1, 'first');
        xb = find(bw(end,:), 1, 'last');
        xc = find(bw(:,end), 1, 'first');
        xd = find(bw(:,end), 1, 'last');
        dab = pdist2([xa, r],[xb, r]);
        dac = pdist2([xa, r],[c, xc]);
        dad = pdist2([xa, r],[c, xd]);
        dbc = pdist2([xb, r],[c, xc]);
        dbd = pdist2([xb, r],[c, xd]);
        dcd = pdist2([c, xc],[c, xd]);
        [mi] = [dab,dac,dad,dbc,dbd,dcd];
        [length, maxidx] = max(mi);
        switch maxidx
            case 1
                coord1 = [xa, r];
                coord2 = [xb, r];
            case 2
                coord1 = [xa, r];
                coord2 = [c, xc];
            case 3
                coord1 = [xa, r];
                coord2 = [c, xd];
            case 4
                coord1 = [xb, r];
                coord2 = [c, xc];
            case 5
                coord1 = [xb, r];
                coord2 = [c, xd];
            case 6
                coord1 = [c, xc];
                coord2 = [c, xd];
            otherwise
                error('strange maximum index!')
        end
    end

[文辉 沈]

I still thank you very much, your help is very useful to me