Matrix call inside a for loop

I probably have an easy equation regarding the correct vector calling inside a for-loop. I’m trying to conduct the same calculation for let’s say different 4 vectors. Therefore I would like to use a for-loop. Simplified, it should look like this:

a_1 = [1 2 3 4 5]

a_2 = [2 3 4 5 6]

a_3 = [3 3 4 5 7]

a_4 = [4 3 4 5 8]

for i=1:4

b(i)=a_(i)/60

end

[José-Luis]

Bad idea. Don't use dynamic variable names, it is horrible code. Use cell arrays instead.

[Stephen23]

a_1 = [1 2 3 4 5]
a_2 = [2 3 4 5 6]
a_3 = [3 3 4 5 7]
a_4 = [4 3 4 5 8]

DO NOT DO THIS. Read this to know why: https://www.mathworks.com/matlabcentral/answers/304528-tutorial-why-variables-should-not-be-named-dynamically-eval

It is much simpler to use a matrix:

a = [1 2 3 4 5; 2 3 4 5 6; 3 3 4 5 7; 4 3 4 5 8]

then your task is trivially easy:

b = a./60

Did you see what I did there? By storing the data in one array I turned your difficult-to-solve task into one trivially easy operation. Writing MATLAB code should be easy, and it is when you store your data in arrays.

[Stephen23]

"I want to invoke different matrix/arrays to use them inside subplot and for further calculations."

We already explained why this is a bad idea: it will make your code slow, buggy, and complex. It is so hard you had to ask on an internet forum for help. Why bother? If you simply stored your data in one array then you can trivially use indexing: indexing is simple, fast, neat, efficient, easy to debug.

[Felix]

 Thanks for your help. 
 %
x = [1 2 2 3 3 4]
y = [0 0 1 1 0 0 ;0 0 2 2 0 0; 0 0 3 3 0 0;0 0 4 4 0 0]
for i=1:4
subplot(2,2,i)
plot(x,y(i,:),'linewidth',2)
axis([0 5 0 5])
end

Answer 1

[Stephen23]

If you simply put all of your data into one array then your task is trivial using indexing:

Time = [0 1 1 3 3 4];
Data = [0 0 2 2 0 0;...
        0 0 3 3 0 0];
cutoff = 1;
idx = Time>=0 & Time <= cutoff;
for k = 1:size(Data,1)
  subplot(2,1,k)
  plot(Time(idx),Data(k,idx),'r','LineWidth',2)
  org = trapz(Data(k,:));
  off = trapz(Data(k,idx));
  out = off ./ org
end

and it displays these outputs:

out =
                    0.25
out =
                    0.25

By using better data design (using one numeric matrix for all data) I wrote more working code in less time than it took you to write your last comment. Good design makes code simpler and more efficient. Ignore whatever bad advice other beginners might give you, do NOT try to access variable names dynamically, doing so is worse code than you can imagine:

https://www.mathworks.com/matlabcentral/answers/304528-tutorial-why-variables-should-not-be-named-dynamically-eval

Answer 2

[José-Luis]

data = {a1,a2,a4,a4}; %Better yet, use a cell array from start
result = cell(size(data));
for ii = 1:numel(data)
    b(ii) = a{ii}./60;
end

You could also use cellfun() to avoid looping.