how can I preallocate for speed in a loop?

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Vickie Guzman
Vickie Guzman on 24 Jan 2019
Answered: StefBu on 24 Jan 2019
Hello,
This is my current code I keep getting an error about pre-allocating my x_p variable.
Would anyone know who I could fix it?
Thank you.
% bisection method
bisection = bisec(depth,x_l,x_u,10,.01);
function ANS = bisec( f, x_l, x_u, itera, error )
%BISEC bisection method
for i = 1:itera
x_p(i) = (x_l + x_u)/2;
if ((f(x_l)*f(x_p(i))) < 0)
x_u = x_p(i);
elseif ((f(x_l)*f(x_p(i))) > 0)
x_l = x_p(i);
elseif ((f(x_l)*f(x_p(i))) == 0)
break;
end
if ((i>1) && (abs((x_p(i)-x_p(i-1))/x_p(i)) * 100) < error)
break;
end
end
ANS = x_p(end);
end

Accepted Answer

StefBu
StefBu on 24 Jan 2019
Hi. Since x_p grows in each iteration of your for-loop you can easily define its size at the begining.
Just use this before your loop:
x_p = zeros(itera,1);
Greetings
Stefan

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