How to find maximum value and corresponding x-value of multiple graphs?

here is my code:

z1=zeros(length(fv),1); 
z2=zeros(length(fv),1); 
z3=zeros(length(fv),1); 
O=zeros(length(fv),1); 
for n=1:length(fv) 
f=(fv(n)); 
om=(2*pi*f); 
om2=(om.*om); 
fhat=((k1+i*om*c1)*Stak)*[0;1;(exp(i*2*pi*L/y));0]; 
A=(K+i*om*C-om2*M); 
zhat=A\fhat; 
z1(n)=zhat(1); 
z2(n)=zhat(2);
 z3(n)=zhat(3); 
O(n)=zhat(4); 
end 
plot(fv,abs(z1),fv,abs(z2),fv,abs(z3),fv,abs(O));  
xlabel('Speed, [m/s]'); 
 ylabel('Displacement, [m]'); 
 grid;  
hold on;

This gives me 4 graphs and i want Identify maxima of the amplitudes (y-values, "z1,z2,z3,O"), and the corresponding vehicle speed (x-values, "fv")

Answer 1

[Rik]

This is trivial if you use an array instead of numbered variables:

z{1}=zeros(numel(fv),1);
z{2}=zeros(numel(fv),1);
z{3}=zeros(numel(fv),1);
%          ^^^^ use numel or size instead of length
O=zeros(nmumel(fv),1); 
for n=1:numel(fv) 
    f=fv(n);
    om=2*pi*f;
    om2=om.*om;
    fhat=((k1+i*om*c1)*Stak)*[0;1;(exp(1i*2*pi*L/y));0];
    %                                  ^^ use 1i or 1j to avoid collision
    %                                  with i as a common variable name
    A=K+i*om*C-om2*M;
    zhat=A\fhat;
    for m=1:3
        z{m}(n)=zhat(m);
    end
    O(n)=zhat(end);
    %         ^^^ this replacement assumes there are only 4 elements
end 
plot(fv,abs(z{1}),fv,abs(z{2}),fv,abs(z{3}),fv,abs(O));
xlabel('Speed, [m/s]');
ylabel('Displacement, [m]');
grid;
%hold on;
% ^^ you aren't adding any plots, so why use hold on?

And now you can use a simple loop to determine whichever maximum you mean exactly.

Instead of a cell array, you could also make z a 2D array:

z=zeros(numel(fv),3);
...
z(n,:)=zhat(1:3);

[martin bjerring]

Thank you!