finding forward direction in matlab

Hi,

I want to write a script for separate forward and backward directions for animal position in a linear track. This is simplified vector.

a = [1 3 5 7 9 10  8 6 4 3 2 3 5 6 7 8 9 7 5 3 2 1];
  m = length(a); 
for i = 2: m-1
     if a(i) >= 1 && a(i-1) > i && a(i+1) > a(i)        
         fstart (i) = a(i-1);   
     end
end

for j = 2: m-1
     if a(j+1) <= 10 && a(j+2) >= a(j+1) && a(j) < a(j+1)
             fend (j) = a(j-1); 
         end   
    
end

The two vectors I want to create is fstart = [1 2] and fend = [10 9] so that later I can combine to have forward vectors [1 3 5 7 9 10] and [ 2 3 5 6 7 8 9].

Please advise me where is wrong.

Thanks in advance!

Answer 1

[KALYAN ACHARJYA]

Please use the another index varibale name inside if statement, like

k=1;
for i=2: m-1
     if a(i)>=1 && a(i-1)>i && a(i+1)>a(i)        
         fstart(k)=a(i-1);
         k=k+1;
     end
end

So that it avoides those extra zero ( MATLAB fills zero in undefined index value of the array). Rest, just use the correct conditional statement in if condition.

[HYZ]

The fstart I would like to have is vector [1 2] as they are the start of ascending order. but the vector I got is [5 7]. Could you help me check why my if condition is wrong? Thanks