How to access alternate elements from a matrrix?

I have a matrix

a =

0 4 5 6 7 .... n

0 0 0 0 0 .....n

I want to access values 0, 5, 7 and do the operation 5-0, 7-5 and so on

Program I have is as follows:

clc

clear

n=input('Enter the number of elements: ');

for i=1:(2*n)+1

x(i)=input('Enter x coordinate of the node');

y(i)=input('Enter y coordinate of the node');

end

a=[x;y]

for i=1:2:n

L(i)=a(1,i+2)-a(1,i);

end

L

I am not getting the desired output. What am Idoing wrong?

Answer 1

[Jan]

a = [0     4     5     6     7;   ...
     0     0     0     0     0]
n = size(a, 2);
for i = 1:n / 2
    k    = (i - 1) * 2 + 1;
    L(i) = a(1, k + 2) - a(1, k);
end

Easier:

L = diff(a(1, 1:2:end))

[Rohit Raut]

Thanks a lot!!!