if a=[1,2,3,4] how can i get b=[ (1+2),(1+3​),(1+4),(2​+3),(2+4),​(3+4) ] using for loops,Thanks

a=[1,2,3,4] 
b=[ (1+2),(1+3),(1+4),(2+3),(2+4),(3+4) ]

[James Tursa]

What have you written so far? What problems are you having with your code?

[MSP]

a=[1 2 3 4 ]

b=zeros(1,10)

for i=1:length(a-1)
    for(k=2:length(a))
     if(i==k)   

          b=a(k+1)+a(i)
       else
          b=a(k)+a(i)
       end
         end
  end

[MSP]

the problem im having is how to access (k+1)th element of a and store them in variable b as rowvector

Answer 1

[James Tursa]

The limits on your first for-loop are not correct. In particular, length(a-1) is not the same as length(a)-1. And the limits on your second for-loop are incorrect as well. You need to start the second loop index at i+1, not hard-coded start at 2. Then, for simplicity, maybe just use a counter to update the appropriate index of b. So, make the following changes:

for i=1:length(a-1)

Make the upper limit length(a)-1 instead of length(a-1)

    for(k=2:length(a))

Make the lower limit i+1 instead of 2 (and get rid of the outer parentheses)

     if(i==k)   
          b=a(k+1)+a(i)
       else
          b=a(k)+a(i)
       end

No need for an if-test here. Simply set the appropriate element of b to your sum. E.g.,

x = 0;  % <-- Do this at the start of your code
    :
      x = x + 1;  % <-- Increment the subscript counter (inside the inner loop)
      b(x) = a(k) + a(i);  % <-- Set the appropriate element of b to your sum

Answer 2

[Guillaume]

Here's an answer without a loop. More efficient!

a = 1:4
b = sum(nchoosek(a, 2), 2)  %use nchoosek(a, 2) to create [1 2; 1 3; 1 4; 2 3; etc.]

[MSP]

Thanks Guillaume.But would u pls provide the crude algorithm using for loops.I would like to clear my confusion regarding looping

[J. Webster]

The purpose of homework is to work out things for yourself. Not to go on messageboards and try to get experts to do your work for you.