MATLAB: Store data from for cycle

store data in nxm array

I need to store the data in an array. I have a plot Y versus the time (tfinal =m) and the Y value is calculated n-times from a n-loop. I need to store the data in mxn array. at the moment I am able to store just 1xn vector, loosing the information on the time. The part of the m.file are the following

index=0
for i=1:Loop
   t=0; %start time 
   t_end=40; %end time
   t_sample=1; %sample interval for gathering data
   ........
   j=1; 
    t_ar(1,t_end/t_sample+1)=0; 
    t_ar(1,j)=t; 
    Y1_ar(1,t_end/t_sample+1)=0; 
    Y1_ar(1,j)=Y1; 
    etc etc
end

Best Answer

you should simply use two for:

    m =5; n=7;
    Mat = zeros(m,n);
    for i = 1:m
        for j = 1:n
             Mat(i,j) = i+j;% what ever
        end
     end

Related Solutions

MATLAB: How to take 100 samples of a plot.

First, what are you actually doing with M, Xdot1, etc.? Currently, the code overwrites them each N_m loop, without doing anything with the results

Try this: define sampled vectors, so you can later vectorize things:

index=randi([100,499],1,N_m);
x1_samp0 = x1(index);
x1_samp1 = x1(index+1);
...
Xdot1=(x1_samp1-x1_samp0)/dt;
...
M(:,1)=1;
M(:,2)=x1_samp0;
...
M(:,6)=x1_samp0.^2;

edit: changed my mind on other option; don't do it. Here are some general tips, though:

if you have a set of conditions that can be expressed as variable=first, variable=second, etc. -- use a switch instead of if-elseif
If you have a loop running over a set of conditions and operations which have nothing else in common -- just run each line individually, then fill in the "else" portion after

for j=1:N_basis
    if j==1
       M(i,j)=1;
    elseif j==2
       M(i,j)=x1(index(i));
    elseif j==3
       M(i,j)=y1(index(i));
    end
end

does the same as the below, but cleaner and faster:

M(i,1)=1;
M(i,2)=x1(index(i));
M(i,3)=y1(index(i));

many, many, many for loops can be replaced with vector operations. It's kinda the point of Matlab

MATLAB: What does for j = [1:i-1, i+1:n] mean

for j = [1:i-1, i+1:n]
  ...
end

is the same as:

for j = 1:n
  if j ~= i
     ...
  end
end

It runs a loop over all numbers from 1 to n, but excludes i . The loop index is the concatenation of the vectors 1:i-1 and i+1:n .

You can simply try it:

n = 10;
i = 7;
for j = [1:i-1, i+1:n]
  disp(j)
end

Best Answer

Related Solutions

MATLAB: How to take 100 samples of a plot.

MATLAB: What does for j = [1:i-1, i+1:n] mean

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