Joint probability
in [Matlab]
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From: Raymond Hoogendoorn on 4 Jul 2010 00:48 Hi all, I have a math problem. I have three vectors of the same length, representing a car's headway S, speed V and a vector (e.g. Z) which can take on the value of 0 or 1 (representing the fact if a driver will take a certain action or not). What I want is to be able to calculate the (joint) probability that a value of 1 in Z occurs at the specific values of S and V. I have no clue how to do this. I tried a lot of options. Please help! Kind regards Raymond
From: Ross on 4 Jul 2010 02:11 "Raymond Hoogendoorn" <r.g.hoogendoorn(a)tudelft.nl> wrote in message <i0p3q3$st6$1(a)fred.mathworks.com>... > Hi all, > > I have a math problem. > > I have three vectors of the same length, representing a car's headway S, speed V and a vector (e.g. Z) which can take on the value of 0 or 1 (representing the fact if a driver will take a certain action or not). > > What I want is to be able to calculate the (joint) probability that a value of 1 in Z occurs at the specific values of S and V. > > I have no clue how to do this. I tried a lot of options. Please help! > > Kind regards > > Raymond If you tell us what you have tried and what you thought was wrong with that, we can give you some relevant help We can't tell whether your problem is with understanding joint probability, or writing matlab code or something else Ross
From: Raymond Hoogendoorn on 4 Jul 2010 02:34 "Ross " <rosswoodskiwi(a)hotmail.com> wrote in message <i0p8lo$7et$1(a)fred.mathworks.com>... > "Raymond Hoogendoorn" <r.g.hoogendoorn(a)tudelft.nl> wrote in message <i0p3q3$st6$1(a)fred.mathworks.com>... > > Hi all, > > > > I have a math problem. > > > > I have three vectors of the same length, representing a car's headway S, speed V and a vector (e.g. Z) which can take on the value of 0 or 1 (representing the fact if a driver will take a certain action or not). > > > > What I want is to be able to calculate the (joint) probability that a value of 1 in Z occurs at the specific values of S and V. > > > > I have no clue how to do this. I tried a lot of options. Please help! > > > > Kind regards > > > > Raymond > > If you tell us what you have tried and what you thought was wrong with that, we can give you some relevant help > > We can't tell whether your problem is with understanding joint probability, or writing matlab code or something else > > Ross Hi, Determining the prob density functions separately for S and V was quit easy. The problem lies in combining them. I've tried a Markov chain approach but that didn't work. My main problem is with programming it in Matlab. However, another problem is that I am a psychologist and not an engineer or expert in math. Kind regards Raymond
From: Steven Lord on 6 Jul 2010 00:09 "Raymond Hoogendoorn" <r.g.hoogendoorn(a)tudelft.nl> wrote in message news:i0pa0t$1t7$1(a)fred.mathworks.com... > "Ross " <rosswoodskiwi(a)hotmail.com> wrote in message > <i0p8lo$7et$1(a)fred.mathworks.com>... >> "Raymond Hoogendoorn" <r.g.hoogendoorn(a)tudelft.nl> wrote in message >> <i0p3q3$st6$1(a)fred.mathworks.com>... *snip* > Hi, > > Determining the prob density functions separately for S and V was quit > easy. The problem lies in combining them. I've tried a Markov chain > approach but that didn't work. > > My main problem is with programming it in Matlab. However, another problem > is that I am a psychologist and not an engineer or expert in math. Why don't you post a SMALL example of your S, V, and Z data and the code you've written to solve the problem? That way the readers can try executing your example and may be able to offer specific suggestions about your code. -- Steve Lord slord(a)mathworks.com comp.soft-sys.matlab (CSSM) FAQ: http://matlabwiki.mathworks.com/MATLAB_FAQ To contact Technical Support use the Contact Us link on http://www.mathworks.com
From: Tom Lane on 6 Jul 2010 15:22 > I have three vectors of the same length, representing a car's headway S, > speed V and a vector (e.g. Z) which can take on the value of 0 or 1 > (representing the fact if a driver will take a certain action or not). > > What I want is to be able to calculate the (joint) probability that a > value of 1 in Z occurs at the specific values of S and V. Like the other responders, I am having trouble understanding what you want. But: Prob(Z,S,V) = Prob(Z) * Prob(S,V|Z) So if you can estimate the marginal probability of Z, and you can estimate the joint probability of S and V separately for each Z value, then you can estimate the joint probability of all three. But from your text description, even though you wrote "joint," it sounds more like you want the conditional probability of Z given values of S and V. I recommend looking up "Bayes theorem" and "conditional probability" in a book or wikipedia or someplace, and see if that helps you formulate the problem. -- Tom
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