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I have been touching on the subject of machine learning out of curiosity, and I have found this weird notation:

if 'f' is a function that does something and 'a' and 'b' are variables, then what does f(a|b) mean?

I know the pipe symbol (|) stands for an OR operation in binary logic, and can stand for the absolute value of a quanitity, the magnitude of a vector, or even the determinant of a matrix. But, I have never seen it been used as such inside a function, except now.

Any help is appreciated.

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    This notation can mean different things depending on the concrete context. Where did you encounter the notation? Can you give a reference? – 2017-01-09
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    It has a very specific meaning in probability, but apart from that, I don't think there are many common, established uses for the notation. – 2017-01-09
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    If $a$ and $b$ are events and $f$ is a probability mass function then $f(a \mid b)$ might be read as "the probability of $a$ given $b$" – 2017-01-09
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    @martini https://en.wikipedia.org/wiki/Pattern_recognition – 2017-01-09
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    In agreement with everybody else that has commented, I say that the notation is not common to all of mathematics, and that there should be a definition of the notation nearby to where you saw it. – 2017-01-09
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    It can also mean "is divisible by" – 2017-01-09
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    Thanks all of you. For this instance, I think Henry got the application of it, given that machine learning is highly based on probability. – 2017-01-09
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    All the examples on that page use 'p' which supports the idea that it is probability. – 2017-01-09

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