Loop and plot in 2D

Hi,

I have a variable V(a,b,c) where

a=1:50

b=a

c=1:100

Now I would like to make a loop and plot the following:

sum_a(V(a,a+r,:))

May I ask you to help me with this loop and the 2D plot?

I have tried with this:

M=50;
V_prev=zeros(a,b,c);
V=V_prev;
 for ik=1:M
     V(ik,:,:)=V+V(ik,:,:);
     for r=50-1:-1:0
        V(ik,ik+r,:)=sum(V(ik,ik+r,:));
     end
 end

Unfortunately it doesn't work.

Thanks in advance for your reply.

[Walter Roberson]

In your duplicate question on this topic, Jan Simon commented:

I do not understand the question. What exactly is "V_a,V_(a+l)"?

Does "sum_a(V(a,a+l,:))" mean:

M = V(1:50, (1:50)+l, :)
sum(M(:))

? What is "l" here? If the 2nd dimension has a length of a, a+l exceeds the array dimensions.

By the way: Do not use "l" (lowercase L) as a name, because it is hard to distinguish from 1.

[Auryn_]

Hi,

yes, it means

M = V(1:50, (1:50)+l, :).

If I sum

sum(M(:)) does it sum in all "l"?

Because I don't want to sum over all "l" but over all a=1:50.

Thank you very much and sorry for any confusion.

[Jan]

@Auryn_: I still do not get it. sum(M(:)) is the sum of all elements of the array M. Where does "l" come into play then?

If V is a V(a,a,b) array and you want to get the sum over all a, than you need:

sum(sum(V, 1), 2)

[Auryn_]

Hi, I have corrected the main text. Hopefully is more clear now! Thanks.

Answer 1

[Image Analyst]

l is a terrible name for a variable. Anyway, you need to make sure a+l is not more than M

if (a+l) > M
      break;
end
V(a,l,:)=sum(V(a,a+l,:));

Answer 2

[Auryn_]

Now it works

for ik=1:a
  for l=100-1:-1:0
    ij=ik+l
    if ij > a
        break;
     end
     A(ik,ij,:)=V(ik,ij,:);
  end
  B(ik,:,:)=sum(A(ik,:,:));
end

[Jan]

I have edited your code. Please read https://www.mathworks.com/matlabcentral/answers/13205-tutorial-how-to-format-your-question-with-markup#answer_18099.

Your code does not run: In the first iteration ik=1 and l=b-1 (did I told you already not to use "l" as name of a variable? It is a really serious advice.) ij is greater than a, such that A is not defined at all. Then the assignment to B fails with an error message.

[Auryn_]

If we consider

a=1:100

and

a=b,

it works.

Thanks again for everything!