Algorithm 1. Pseudo-code of CEFO algorithm

/* Part 1: Algorithm parameters initialization */

$N\_var$: The number of electromagnets in each electromagnetic particle.

$N\_emp$: The number of electromagnetic particles in population.

$Ps\_rate$: The probability of changing one electromagnet with a random electromagnet.

$R\_rate$: The probability of selecting electromagnets from the positive field.

$P\_field$: The portion of particles belonging to positive.

$N\_field$: The portion of particles belonging to negative.

min = lower boundary; max = upper boundary

/* Part 2: Main loop of the algorithm */

for i = 1 to $N\_emp$ do

for j = 1 to $N\_var$ do

position [i, j] = min + rand ( )$\ast$(max − min)

end for

end for

Update position by using the chaotic map of Equation (5)

fitness = function (position)

while t (current iteration) < max iterations

Divide the electromagnetic field into three regions

for i = 1 to $N\_var$ do

if rand (0,1) > $Ps\_rate$

Generate the $EM{P}^{New}$ by Equation (4)

else

Generate the $EM{P}^{New}$ from positive particles

end if

Check if any particle beyond the search space

end for

if rand (0,1) < $R\_rate$

Change one electromagnet of $EM{P}^{New}$ randomly

end if

Compare the fitness of $EM{P}^{New}$ with worst particle

t = t + 1

end while

Output the best particle