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For some reason, I need to have a program that will make a small no. of mistakes every now and then, and I should not know what mistakes it has made and when.

I do not need it to make multiple mistakes in one set(run of the algorithm), but rather I plan on making (say) 10,000 runs of the program, and I need it to make mistakes 200 times ..

Very importantly, I must be sanguine that there are no more than (1/5)n mistakes, where n is the total no. of results generated using the program.

The results that I am talking about here can be anything that is quantifiable and verifiable, like eg. an array of values.

Doing something like this:

for(int i=0; i<10000; i++)
   //one fifth of the times put garbage in the array using random function!!
   for (int j=0; j<5; j++)
      array[j]=j;

is too simplistic and not real enough.

So I thought may be I must look for a mathematical function that can do this for me. Any ideas ?

P.S. I am a noob at math (struggled with engineering college math). So please elaborate your answer. Dont say something like "Use XXX'YYY theorem .." I might not understand! Also, plese attach proper taf to this question. I could not thing of any ..

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What do you mean by real enough? Maybe define a set of mistakes that you choose from-swap a pair of values in the array, change just one value in the array, change all the 0's in the array to 1's? –  Ross Millikan Jan 10 '12 at 14:06
1  
So, something like if (rand() < 0.2) then, then? –  J. M. Jan 10 '12 at 14:07
    
@J.M. Sorry, cant use that. (I think this was clear enough from my code sample) –  Wildling Jan 10 '12 at 15:47
4  
No, it wasn't; you haven't said anything about conditionals not being allowed. –  J. M. Jan 10 '12 at 15:51
2  
Are @RYUZAKI and drunkMonk the same person? –  Rahul Jan 10 '12 at 16:58

1 Answer 1

up vote 1 down vote accepted

Sometimes a programming language will allow picking a (pseudo-)random item from a list. If you can the following pseudocode seems to do what you want:

  1. BigList is the complete list of the number of runs, say 10000.

  2. For $i$ = $1$ to $200$.

  3. Pick $n$ from BigList. (This uses the item picking function)

  4. Replace BigList with BigList $\smallsetminus \{ n \} $. (Delete $n$ from BigList)

  5. End For (At the end of the for loop we now know which runs should have an error.

  6. Do $i$ = $1$ to $10000$.

  7. If $i$ is still in BigList do the right thing, else do the wrong thing.

  8. End Do.

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