Editing Probability mass function (section)

==Formal definition==
Probability mass function is the probability distribution of a  [[discrete random variable]], and provides the possible values and their associated probabilities. It is the function <math>p: \R \to [0,1]</math> defined by
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for <math>-\infin < x < \infin</math>,<ref name=":0" /> where <math>P</math> is a [[probability measure]]. <math>p_X(x)</math> can also be simplified as <math>p(x)</math>.<ref>{{Cite book|title=Engineering optimization : theory and practice| last=Rao | first = Singiresu S.|date=1996|publisher=Wiley|isbn=0-471-55034-5|edition=3rd|location=New York|oclc=62080932}}</ref>

The probabilities associated with all (hypothetical) values must be non-negative and sum up to 1,

<math display="block">\sum_x p_X(x) = 1 </math> and <math display="block"> p_X(x)\geq 0.</math>

Thinking of probability as mass helps to avoid mistakes since the physical mass is [[Conservation of mass|conserved]] as is the total probability for all hypothetical outcomes <math>x</math>.