Hello, It's pudding!! I'm new with Matlab and i'm using old version 2011a!!

Hello everyone ;

Please I need a help, i wrote a general code for determining natural frequencies and shape modes,but during the execution, i got a problem, no figure!!!

My pleasure if someone help me, please!! here is the code which i wrote it!!

%%%%----------------General Code-------------------%%
clear
clc
close all
n=input('degrees of freedom');  %----le nombre des masses--- 

Error using input
Support for user input is required, which is not available on this platform.

M=zeros(n,n);
for i=1:n
    M(i,i)=input('input la masse d elemnt');
end
K=zeros(n,n);
disp('0 = pas deconnection');
for i=1:n
    K(i,i)=input('element de la raideur connecté à la terre');
end
for i=1:n-1
    for j=i+1:n
        k=input('connection entre les elements de raideur');
        K(i,i)=K(i,i)+k;
        K(i,j)=K(i,j)-k;
        K(j,i)=K(j,i)-k;
        K(j,j)=K(j,j)+k;
    end
end
%%----------Calcul de vitesse angulaire naturelle---------%%
[V,D]=eig(K,M);
omega=diag(D).^0.5;
freq_nat=omega/2*pi;
F = cell(numel(n),1);%%-- forces' vectors%%
%%%%%---------Determination of eigenvalues--------%%%
C=zeros(n,n);
disp('0 = pas deconnection');
for i=1:n
    C(i,i)=input('element d amortisseur connecté à la terre');
end
for i=1:n-1
    for j=i+1:n
        k=input('connection entre les elements damortisseur');
        C(i,i)=C(i,i)+k;
        C(i,j)=C(i,j)-k;
        C(j,i)=C(j,i)-k;
        C(j,j)=C(j,j)+k;
    end
end
%%%%------------Fréquences propres amorties---------%%%   
A=[zeros(n,n),M;M,C]; 
B=[-M,zeros(n,n);zeros(n,n),K];
[V,D]=eig(full(B),full(A));
[omega,tmp]=sort(sqrt(diag(imag(D))),'ascend');
freq_nat=omega/2/pi;
[mode,tmp]=sort((V),'ascend');
%%%for i=1:n
    %%V(:,i)=V(:,i)/V(n,i);
%end
for i=1:length(D)
 zeta(i)=-(real(D(i)))/(imag(D(i)));
end
for i=1:length(D)
 plot(freq_nat(i),zeta(i));
 xlabel('frequences naturelles');
 ylabel('coefficient damortissement');
end
for i=1:length(V)
    plot(V(:,i));
    figure()
hold on
title('mode (i)')
hold off
 xlabel('overturning moment');
 ylabel('');
end

[Walter Roberson]

A=[zeros(n,n),M;M,C]; 
B=[-M,zeros(n,n);zeros(n,n),K];

None of the values you are putting together here are sparse(), so A and B are not going to be sparse.

[V,D]=eig(full(B),full(A));

There is no point in calling full() on arrays that are not sparse.

Answer 1

[Walter Roberson]

for i=1:length(D)
 plot(freq_nat(i),zeta(i));

You are plotting a scalar against a scalar in each iteration. By default, plot() adds no markers and only joins points if there are at least two adjacent finite points. By plotting a scalar against a scalar, at no time are you asking plot to plot two adjacent finite points... so plot() is plotting nothing.

You have two choices: You can either request a marker, or you can ask to plot() multiple points.

In the case of asking for a marker, you would add a specification such as '*' to your plot() call, making it something like

 plot(freq_nat(i), zeta(i), '*');

But... if you are going to plot() a bunch of scalars within a loop, with markers for each, you might as well plot() an entire vector of points at one time outside of any loop, by requesting

 plot(freq_nat, zeta, '*')

not in a loop. Unless, that is, you really want each separate point to be a distinct color (and if so then you are better off using scatter())

Plotting multiple points with lines joining the points is just

 plot(freq_nat, zeta);

not in a loop.

[Amira]

@Walter Roberson Thank you so much for ur help!! i do appreciate it ! it works !!