Databases
StackOverflow2013
Postsdbo
PO
 

Note that there are some explanatory texts on larger screens.

plurals
  1. PO
    primarykey
    data
    text
    <p>The concept you're looking for is called "roulette wheel selection." You don't have an established fitness function yet (you may be implying that the fitness of each individual is the integral value of its chromosome), but when you do a general plan is:</p> <ol> <li> Sum the fitness of the entire population.</li> <li> Get a random number (call it x) between 0 and the total fitness.</li> <li> Iterate through the population. For each member: <ol> <li> Subtract the member's fitness from x.</li> <li> If x is now less or equal to zero, select the current member.</li> </ol> </ol> <p>There are other equivalent implementations, but the general idea is to select members with a probability proportional to their fitness.</p> <p>Edit: A few notes on fitness functions. The representation of a chromosome (in your case as a 32-bit integer) is independent of the fitness function used to evaluate it. For example, binary encodings typically treat the chromosome as a set of bitfields packed into an integral value of appropriate size. Crossover and mutation can then be accomplished by the appropriate bit-masking operations. If you're interested, I can post some simple GA code I have laying around (in C and Python) which uses bitwise operations to implement these functions. I'm not sure how comfortable you are with these languages.</p>
    singulars
    1. This table or related slice is empty.
    1. POGA written in Java
      singulars
      1. PTQuestion
    1. PTAnswer
    1. USDerrick Turk
    1. USDerrick Turk
    plurals
    1. This table or related slice is empty.
    1. This table or related slice is empty.
    1. This table or related slice is empty.
    1. This table or related slice is empty.
    1. VO
      singulars
      1. PO
      1. This table or related slice is empty.
      1. VTUpMod
    1. COPart three is where I have the problem. I have my population and its genes, I have given them each a number that is either zero or one and I have a sum of the total fitness of the entire population. Do I now loop through the same thing again and if I do so what member do I select? To answer your latest question I am familiar with C, although at the moment I am just struggling with the fitness method; I have a pretty good idea of how I will handle the crossover and mutation.
      singulars
      1. PO
      1. USMike B
    2. COSorry, just took another look at your code. You've got each chromosome as an array of int, each of which is to be either 0 or 1. When I skimmed the first time, I assumed you were packing alleles as bits into a single integer, which would be more space-efficient. The fitness function represents your best guess as to how "good" an individual solution (=chromosome) is. My roulette wheel selection psuedocode assumes that fitness is to be maximized rather than minimized, but it's easily altered for the opposite. (To be continued...)
      singulars
      1. PO
      1. USDerrick Turk
    3. COYou would (after computing the total fitness---your current "fitness function" is that a chromosome's fitness is the sum of it's int array) loop back through your population. Here is a simple GA I have previously written as a demonstration in C: <a href="http://codepad.org/f8IJiCu1">http://codepad.org/f8IJiCu1</a>. It may help to see some code as the algorithm can be difficult to explain in writing. A similar Python version I wrote is at: <a href="http://codepad.org/8imFTytY">http://codepad.org/8imFTytY</a>. This is a little cleaner IMHO.
      singulars
      1. PO
      1. USDerrick Turk
 

Querying!

 
Guidance
A row detail

Detail views are divided into sections. All the information in the data section comes from columns in the selected row. The other sections display data from other, related rows.

Related data can be related in a to-one or a to-many fashion. Captions of data related in a to-many fashion link to a list view showing a filtered view of the table.

Try moving around until you find a non-empty to-many entry and click on the label to get to one. You can move back to the root by clicking on the database name in the header.

SQuiL has stopped working due to an internal error.

If you are curious you may find further information in the browser console, which is accessible through the devtools (F12).

Reload