Using the value of the next step in a FOR loop over a vector

Hi everybody,

is it possible to use in a for loop over a vector the value of the next step?

e.g. if got a vector like this:

h_x=[0 0 0 -2 -15 -100 -50 50 0 0 0 0]

and a loop using the vector

for test=h_x
    if test==0
        disp('No')
    else
        if test-1 ==0
            a=test %when the value of the step before was 0, it should just use the value of the current step without any operations into a new Vector 'a'
        if test+1 ==0
            a=test %when the value of the step after is 0, it should just use the value of the current step without any operations into a new Vector 'a'
        end
        end
        
        a=h_x+(10*(test+1))+(10*(test-1)) %Here the current value and 10 times the value of the vector step befor and after should be put into the new vector 'a'
    end
end

This should result in a vector a like this:

a=[0 0 0 -2 (-15+(10*-2)+(10*-100)) (-100+(10*-15)+(10*-50)) (-50+(10*-100)+(10*50)) 50 0 0 0 0]
a=[0 0 0 -2 -1035 -750 -550 50 0 0 0 0]

Does anyone has a hint for me how to include the next steps of the for loop into the formula?

Thank you in advance and very best

Christian

Answer 1

[Stephen23]

"Does anyone has a hint for me how to include the next steps of the for loop into the formula?"

In MATLAB it is much better to loop over indices, rather than looping over data values. Then your task is easy:

h_x = [0,0,0,-2,-15,-100,-50,50,0,0,0,0];
a = h_x; % preallocate
for k = 2:numel(h_x)-1 % loop over indices!
    v = h_x(k-1:k+1);  % sub-vector
    if all(v([1,3]))   % non-zero
        a(k) = v*[10;1;10];
    end
end

giving:

>> out
out =
      0      0      0     -2  -1035   -750   -550     50      0      0      0

Or you could avoid the loop entirely:

>> x = [0,h_x(1:end-1)];
>> y = [h_x(2:end),0];
>> z = x&y; % non-zero
>> a = [10,1,10]*[x.*z;h_x;y.*z]
a =
      0      0      0     -2  -1035   -750   -550     50      0      0      0

[Christian S.]

That was fast, thank you very much!