Error message when running code: "Dimension argument must be a positive integer scalar"

I have this error message and i don't know what to do please help?

Error using size

Dimension argument must be a positive integer scalar or a vector of positive integers.

Error in practice (line 36)

x=zeros(size(n,q));

The code:

clear;
m1=3000;k=13650;
mass=[m1,0,0;0,4*m1,0;0,0,m1];
M=input('mass');
[n,o]=size(M);
if n~=o 
    error('mass');
end
stiff=[k+k,-k,0;-k,k+k,-k;0,-k,k+k];
K=input('stiff');
[n,o]=size(K);
if n~=o 
    error('stiff');
end
qu=0;
[u,l]=eig(K,M);
% Using eigin this way allows us to subtract M*w^2
% from K, instead of I*w^2 (where I is the n by n identity
% matrix).
% The output from eiggives unit-length eigenvectors.
% We need to scale them with respect to M.
%
for s=1:n
    alfa=sqrt(u(:,s)'*M*u(:,s));
    u(:,s)=u(:,s)/alfa;
end
inid=[0;0;0];
iniv=[0;0;0];

x0=input('inid');
xd0=input('iniv');
final=[];
tf=input('final');
t=0:0.1:tf;
q=tf/0.1;
x=zeros(size(n,q));
% Applying Equation 7.183.
%
for j=1:n
    w(j)=sqrt(l(j,j));
    xt=u(:,j)*(u(:,j)'*M*x0*cos(w(j).*t)+u(:,j)'*M*xd0/...
        w(j)*sin(w(j).*t));
    x=x+xt;
end
% Plotting the modes in a subplot format.
% Note that, for more than 3 or 4 degrees
% of freedom, the plots will become nearly
% unreadable.
%
for r=1:n
    subplot(n,1,r)
    plot(t,x(r,:))
    xlabel('Time, seconds');
    ylabel(['Response x',num2str(r)]);
end

Answer 1

[Chandler Hall]

x=zeros(size(n,q))

Perhaps you intend:

x = zeros(size(n, 1), numel(t));

[Walter Roberson]

As a special case you can just use x=0; in this context.

[Abdalrazzaq Aljammal]

thak you sir its worked.

Answer 2

[Image Analyst]

What values did you enter? I entered 4, 5, 4, 4, and 4 and got no such error with the code above.

Are you sure you actually entered a number and didn't just hit Enter (to give a null value)?

Also, n and q need to be integers. So you might correct

q=tf/0.1;
x=zeros(size(n,q));

to this

q = 10 * tf;
x = zeros(size(n, q));

Why? See the FAQ:

https://matlab.fandom.com/wiki/FAQ#Why_is_0.3_-_0.2_-_0.1_(or_similar)_not_equal_to_zero?