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### Re^3: Travelling problem (Anyone better 86850?)

by BrowserUk (Pope)
 on Dec 23, 2013 at 15:40 UTC ( #1068206=note: print w/replies, xml ) Need Help??

in reply to Re^2: Travelling problem (Anyone better 86850?)

Quite ruthless really. First time I have tried this approach, seems very powerful.

You mustn't be too ruthless though. You have to allow some of the less good candidates to evolve otherwise the algorithm will lock into a local minima and never explore further.

For example, there are at least 8 better solutions than the 86850:

```84860
85075
85294
85469
85509
85684
85982
86197

But these will never be discovered by minor evolution from the 86850 solution.

You have to allow some radical variations (with significantly less good scores) to evolve for a while to discover these better ones.

With the rise and rise of 'Social' network sites: 'Computers are making people easier to use everyday'
Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error.
"Science is about questioning the status quo. Questioning authority".
In the absence of evidence, opinion is indistinguishable from prejudice.

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Re^4: Travelling problem (Anyone better 86850?)
by tangent (Vicar) on Dec 23, 2013 at 16:37 UTC
By widening the net, and a bit more shuffling I get:
```84860
85075
85294
85469
85489
85509
85684
85923
Re^4: Travelling problem (Anyone better 86850?)
by tangent (Vicar) on Dec 23, 2013 at 15:47 UTC
That makes sense. I found I had to keep adding variations to avoid dead ends, the shuffles in particular helped. How would you choose those 'radical variations'? At random from the laggards, or according to some other criteria, some way of spotting potential?
How would you choose those 'radical variations'?

I haven't found a good method yet. So far I've tried:

• Swapping pairs of nodes for the top N so far.
• Shuffling the nodes between two random points for the top N so far.
• Reversing the nodes between two random picks for the top N so far.
• Adding N new totally random shuffles to the set being evolved.

None of these seems to prevent the local minima phenomena.

The best approach I've found is once the top N stop changing; throw them all away (remembering the best 1) and start over with a completely new set of random picks.

With the rise and rise of 'Social' network sites: 'Computers are making people easier to use everyday'
Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error.
"Science is about questioning the status quo. Questioning authority".
In the absence of evidence, opinion is indistinguishable from prejudice.

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