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I am currently reading a paper on a meta-heuristic called 'Grasshopper Optimization Algorithm'.

The main idea of the algorithm is to utilize the social behavior of grasshoppers in a swarm to solve optimization problems. The distance to other grasshoppers in the swarm is used to determine, if a grashopper is repelled (exploration) or attracted (exploitation) from grasshoppers in its proximity.

However I am not sure if I understood the first part of the proposed formula correctly:

$$X_i^d = c\left(\sum\limits_{j=1,j\neq i}^Nc\frac{ub_d-lb_d}{2}s\left(\lvert x_j^d-x_i^d\rvert\right)\frac{x_j-x_i}{d_{ij}}\right) + \widehat{T}_d$$

$X_i^d$ calculates the next position of a search agent (grasshopper) with respect to the postion of the other search agents and the best found solution so far. So the next position of a grasshopper depends on its own position, the positions of all other grasshoppers in the swarm and the best solution found so far.

$\widehat{T}_d$ denotes the best solution found so far.

$c$ is a decreasing coefficient that regulates if the search agents explore or exploit in the search space. With increasing iteration count $c$ decreases and the search agents tend to exploitation.

$s\left(\lvert x_j^d-x_i^d\rvert\right)$

The part in brackets calculates the distance between grashoppers. $s$ is a formula which takes this value and determines if the search agents should explore or exploit.

$\frac{x_j-x_i}{d_{ij}}$ is a unit vector, where $d_{ij}$ denotes the distance between two grasshoppers.

It states that $ub_d$ is the upper bound and $lb_d$ is the lower bound in the $d$-th dimension. It further states that the part $c\frac{ub_d-lb_d}{2}$ linearly decreases the space that grasshoppers (search agents) should explore and exploit.

I dont undertsand what is meant with 'upper and lower bound in the $d$-th dimension'. Upper and lower bound for what exactly?

Can somebody help?

Information extracted from this paper:

Grashopper Optimization Algorithm

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  • $\begingroup$ Please give some context to understand the meaning of the formula and notations. $\endgroup$
    – Nathaniel
    May 3, 2021 at 10:26
  • $\begingroup$ @Nathaniel I tried to condense the information, I hope this helps. $\endgroup$
    – gython
    May 3, 2021 at 11:32

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I suspect they probably mean $$ub_d = \max_i x_i^d$$ where $x_i^d$ is the $d$h coordinate of $x_i$; and similarly for $lb_d$, but using $\min$ instead of $\max$. But I don't know -- I am just speculating based on context.

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  • $\begingroup$ Thanks for your answer! Would $max \ x_i^d$ be the max coordinate of the grasshopper (value to be optimised) in the swarm in the current iteration? $\endgroup$
    – gython
    May 3, 2021 at 20:18
  • $\begingroup$ @gython, max value over all grasshopppers in that coordinate $\endgroup$
    – D.W. ♦
    May 3, 2021 at 20:34
  • $\begingroup$ How I understood the algorithm, it states that 2 grasshoppers cant be on the same position, because if they are too close to each other, they repel each other $\endgroup$
    – gython
    May 3, 2021 at 21:32

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