I have a double variable equation with the values of x(a) and y(b), I am asked to find the maximum values(done) . Then I need to find which values of y are where the maximum happens. The problem is that the equation matriz(D) is 300 x 100.

a   = 0.01:0.01:1;      na = length(a);
b = 0.01:0.01:3;      nb = length(b); 

D = zeros(nb,na); 

for k=1:nb
   for J=1:na
        D(k,J)=(1/sqrt((((1-(b(k)).^2).^2)+(2*a(J)*b(k)).^2)));
   end
 end

s  = max(D,[],1);

%figure;
%plot(b,D); xlim([0 3]); ylim([0 10]);  
%xlabel('B'); ylabel('D');

%figure; 
%plot(a,s,'-bo','Markerfacecolor','g', 'Linewidth',2); 
%xlim ([ 0 1]); ylim ([0 10]); xlabel ('razón de amortiguamiento');

Answer 1

[Sargondjani]

[s, index]=max(D,[],1);

your s contains the maximum value for each column, the index contains the row number. So b(index) gives you the corresponding value

(you can also get the maximum of the whole matrix by applying the 'max' twice)

Answer 2

[Andrei Bobrov]

a   = 0.01:0.01:1;
b = 0.01:0.01:3;
[jj,k] = ndgrid(b,a);
D1 =  1./hypot(  1-jj.^2, 2*k.*jj );
[~,imx] = max(D1(:));
out = b(rem(imx-1,size(D1,1))+1)