How to save part of the data in text file?

I have the following plots at different time steps, I would like to save the data at the last time step in a text file. How can I simply do that?

For example my plotting section, I am saving the data into a multi-dimenional array that has the 3rd dim as t and would plot my data in three different timesteps. How can I save data in a text file at timestep 0.12 at the plots example and not the entire data.

Code:

t = 0;
step = 0;
hstep = 1;
wstep = 1; 
while t < tend && step < N_max
    [U_T, t] = MacCormack(U_T, gamma, t, dx, CFL, sigmma); 
    step = step + 1;
    if mod(step,wstep) == 0 
        U_TData(:,:,hstep) = U_T; % How to save this data in text file?
        Vp_Data(:,:,hstep) = C2P( U_T, gamma ); 
        hstep = hstep+1;
        t_Data(hstep) = t;
    end
   
end    
shiste = size(U_TData);
numframe = shiste(3);
iterframe = floor(numframe/3);
f1 = figure();
subplot(2,2,1)
for i = 1:3
    plot(x,U_TData(1,:,i*iterframe))
    hold on
    Legend{i} = strcat('t=', num2str(t_Data(i*iterframe),'%.2f'));
end

Plots:

Answer 1

[Scott MacKenzie]

If you want to save the data being plotted on the last iteration (i = 3), try adding one line after your loop:

for i = 1:3
    plot(x,U_TData(1,:,i*iterframe))
    hold on
    Legend{i} = strcat('t=', num2str(t_Data(i*iterframe),'%.2f'));
end
writematrix([x U_TData(1,:,3*iterframe)], 'name_of_file.txt');

[Jamie Al]

Thanks! This would save both U_TData and x or just x?

[Scott MacKenzie]

Both

[Jamie Al]

Thanks