summation of diffrent lengths in vector

I would like to sum some lengths in vector. For example I have a=[0.0 0.0 0.3 0.4 0.5 0.0 0.0 0.0 0.0 1.0 1.1]. I need b=((0.5-0.3)+(1.1-1.0))=0.3. The time step is constant=0.1 and this order of elements can be change in new run of the program.Thanks alot.

[Grzegorz Knor]

According to what rules you want to sum up? Could you explain?

Answer 1

[Clemens]

I would do this with some logical indexing magic.

a=[0.0 0.0 0.3 0.4 0.5 0.0 0.0 0.0 0.0 1.0 1.1];
step = 0.1;
tmp = a>0; % rule what elements to take
i_sum = tmp(1:end-1) & tmp(2:end)>0; % magic removes 1 element from each group
distances = sum((i_sum))* step % = 0.3

[Sakhr]

It works fine,really magic, thanks for help