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MathGroup Archive 2011

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Re: Coin Toss Simulation

  • To: mathgroup at smc.vnet.net
  • Subject: [mg122374] Re: Coin Toss Simulation
  • From: "Tony Harker" <a.harker at ucl.ac.uk>
  • Date: Thu, 27 Oct 2011 06:27:51 -0400 (EDT)
  • Delivered-to: l-mathgroup@mail-archive0.wolfram.com

The problem is that you use Set Delayed (:=) everywhere rather than Set (=).
This means that neither s nor g are evaluated until they are used. So, when
{g,s} is calculated this is what happens:
  1. a value is calculated for g, and becomes the first element of the list
  2. with that done and dusted, Mathematica moves on to compute s.
    i) s requires a value for g, so
   ii) compute a new value for g (because of the SetDelayed)
  iii) count the heads
 iv) make that the second element of the list.

  As a result, the list of heads and tails and the count of heads in the
returned answer do not correspond.

 This would work:
y[n_] := Block[{g, s}, g = RandomChoice[{"head", "tail"}, n];
  s := Count[g, "head"];
  {g, s}]

Or, neater perhaps,
 y[n_]:={#,Count[#,"head"]}&[ RandomChoice[{"head", "tail"}, n]]
 
   Tony

]-> -----Original Message-----
]-> From: pooleman133 [mailto:poolebc221 at gmail.com]
]-> Sent: 26 October 2011 22:39
]-> To: mathgroup at smc.vnet.net
]-> Subject: Coin Toss Sim
]-> 
]-> I am new to mathematica and am trying to make a coin flipping simulation
]-> however mo code isn't working. When I tell it to count the number of
head
]-> it gives me a bad count. The code I am using is listed below any help
would
]-> be greatly appreciated.
]-> 
]-> y[n_] := Block[{g, s},
]-> 
]-> 
]->   g := RandomChoice[{"head", "tail"}, n];
]->   s := Count[g, "head"];
]->   {g, s}
]->   ]





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