loop over a matrix by taking the previous index

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bbah
bbah 2019-11-20
评论： bbah 2019-11-20
hi,
i want to loop over a matrix and add the element to a row by taking the index of the previous element.
e.g.
first_element = find(gnbh(:,1) == 0 ) %now i have the first element i need
i = 1:length(first_element)
j = first_element(i)
next_element = gnbh(j,2)
next_element1 = gnbh(next_element,2)
next_element2 = gnbh(next_element1,2)
and so on ... until my next_element is 0
in the end i want to add to every element j the element next_element,next_element1,next_element2 ...
i hope somebody can help me
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Guillaume
Guillaume 2019-11-20
What is the significance of the number in the first column? It doesn't appear to have any meaning? other than maybe you want to start at every 0. The non-zero values of the first column don't appear to be used anywhere.
bbah
bbah 2019-11-20
good question. the 0 in both columns actually stays for a different type of elements. that means for every 0 the neighbour element in +x or -x direction will be a completely different type of element which im not interested in. absolutely no neighbour would be -1.
what i am trying to do is to collect the elements by starting at -x = 0 ( which means my next element in -x direction is not my type of element) and add every element until i reach my last element ( which means my next element in x direction would be again a different element and it has the value +x=0)
with the loop i did in the beginning i can get the 1st elements that start at -x=0 and my next elements at +x but i dont know how to get from my next element the next element in +x direction until i reach +x=0.
i hope u can understand me

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