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How to optimise this code?
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Nested loops suck...how can I optimise this code?
function [a, v, x] = model1(x_s, x_a, OB, rho_0, K_a, K_r, K_v)
ss = 0.01; % Step Size
tmax = 60;
c = 0; % Row index ID (for identification only)
k = 1:length(OB); % Vectorisation
x = [x_s(1); x_s(2)]; % Initial position
v = [0; 0]; % Initial velocity
a = [0; 0]; % Initial acceleration
dUa = [1; 1];
while ((dUa(1)^2 + dUa(2)^2) > 1e-10) && (c <= (tmax/ss)+1)
dUr = 0; % Reset the force
c = c + 1; % Add one to the row count (first iteration c = 1)
dUa = K_a*(x(:,c) - x_a); % Calculate attractive force
% Calculate distance from each obstacle
rho_r = sqrt( (x(1,c)-OB(1,k)).^2 + (x(2,c)-OB(2,k)).^2 );
for numobs = 1:length(OB) % Loop for the number of obstacles created
if rho_r(numobs) > rho_0 % If outwith the obstacle radius
dUrobs = 0; % No force experienced
else % Otherwise
dUrobs = K_r * ((1/rho_r(numobs)) + (1/rho_0)) * (OB(:,numobs)-x(:,c))/(rho_r(numobs)^3);
end
dUr = dUr + dUrobs; % Combine force from each obstacle to total
end
a(:,c+1) = -dUa - dUr - K_v * v(:,c); % Calculate acceleration
v(:,c+1) = v(:,c) + a(:,c+1) * ss; % Calculate new velocity
x(:,c+1) = x(:,c) + v(:,c+1) * ss; % Calculate new position
end
0 Kommentare
Antworten (1)
Jan
am 24 Jan. 2016
Pre-allocation!
n = ceil(c <= (tmax/ss) + 1);
x = zeros(2, n);
x(:, 1) = x_s(1:2); % Initial position
v = zeros(2, n); % Initial velocity
a = zeros(2, n); % Initial acceleration
...
The power operation is expensive, so do not compute it repeatedly: Omit zeros in the sum:
rho_r3 = rho_r ^ 3;
...
for numobs = 1:length(OB) % Loop for the number of obstacles created
if rho_r(numobs) <= rho_0 % If outwith the obstacle radius
dUr = dUr + K_r * (1/rho_r(numobs) + (1/rho_0)) * ...
(OB(:,numobs)-x(:,c)) / rho_r3(numobs);
end
end
Crop the unused memory at the end:
x = x(:, 1:c);
v = v(:, 1:c);
a = a(:, 1:c);
2 Kommentare
Jan
am 31 Jan. 2016
Maybe. But it is not worth to spend hours in optimizing the code, when you save some seconds of runtime only. You can try this instead of the "for numobs" loop:
K = (rho_r <= rho_0);
dUR = sum(K_r .* (1 ./ rho_r(K) + 1 ./ rho_0) .* ...
(OB(:, K) - x(:, c)) ./ rho_r3(K));
I cannot debug this due to the missing input data. Maybe some vectors must be transposed. But there migt be further problems with the sizes. Anyway, the underlying method is cleared.
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