this program taking a long time to run and i did't get the answer also due to this problem. how can i reduce this time

my data contain 1182614X3 datas, s=[]; x=data(1:end,1); y=data(1:end,2); z=data(1:end,3); x1=5; x2=9; y1=10; y2=14; z1=25; data2=[x1 y1 z1]; mainslope=(y2-y1)/(x2-x1); count=length(x); for i=1:count x3=x(i); y3=y(i); slope=(y3-y1)/(x3-x1); s=[s;x3 y3 slope]; if slope==mainslope z3=z(i); data2=[data2; x3 y3 z3]; end end

Answer 1

[Jos (10584)]

The slowness is caused by the fact to you expand the matrix s and sometimes the matrix data2 in each iteration. You should preallocated these. I also removed the if-end construction as you can easily weed out the unwanted values of data2 afterwards.

    x=data(1:end,1); y=data(1:end,2); z=data(1:end,3); 
    x1=5; x2=9; y1=10; y2=14; z1=25; 
    mainslope=(y2-y1)/(x2-x1);
    count=length(x); 

    % pre-allocation
    s = nan(count,3) ;
    data2 = nan(count+1,3) ; % apparently, data2 can become 1 longer than s ...
    data2(1,:) = [x1 y1 z1]; 

    for i=1:count 
       x3=x(i); y3=y(i); 
       slope=(y3-y1)/(x3-x1); 
       s(i,:) = [x3 y3 slope] ;
       data2(i+1,:) = [x3 y3 z(i)] ;
    end
    TF = s(:,3) == mainslope ; % OR abs(s(:,3)-mainslope) < 0.001 ???
    data2 = data2([true ; TF],:) ; % only retain when slope equals mainslope (plus the first row)