MATLAB: How to find the first element that satisfy a condition in a matrix

findif condition

Hallo,
I have a matrix describes the difference between secuencial elements Dwf (127*2398).
now I want to find out the first element (column-wise) that satisfy the condition < 0.01 then starting from this element I want to find the first element that is < 0 and make a new matrix limited with the elements bewteen this two conditions as in the following : ( first_element : last_element +1)
I have tried some coding but it didn't work out so far, I am still a beginner with MATLAB.
hope someone could help and thatnks in advance 
for i=6:127 % the rows, I must start from the 6th row
    for j = 1:2700 % the columns
first_element(:,j) = find(Dwf(:,j)> 0.01,1,'first'); 
last_element(:,j) = find(Dwf(:,j) < 0 & j > first_element,1,'first') ;
    end
end

Best Answer

Try this
for j = 1:ny
    idx_start(:,j) = find(Dwf(:,j)> 0.01,1,'first') ;   
    idx_end(:,j) = find (Dwf(:,j) < 0 & (1:nx)' > idx_start(:,j) , 1, 'first'); 
end
Related Question