first, expectation and varianceVariance According to mathematical expectations there are two formulas: dx=e ((X-ex) ^2) and dx=ex^2-(EX) ^2
dx=e (x^2-2xex+ (EX) ^2)
=e (x^2)-E (2XEX) + (EX) ^2
=e (x^2) -2 (ex) ^2+ (ex) ^2
=e (x^2)-(EX) ^2
Second, poisson distribution The probability function of the Poisson distribution is:
The parameter λ of the Poisson distribution is the average occurrence of random events in the unit time (or unit area). Poisson distribution is suitable for describing the number of random events that occur in a unit time。the expectation and variance of the Poisson distribution areThe feature function isThe Poisson distribution is suitable for describing the number of random events occurring within a unit of time (or space). If a service facility arrives in a certain amount of time, the number of calls received by the telephone switch, the bus stationThe number of guests in the station, the number of failures in the machine, the number of natural disasters, the number of defects on a product, the number of bacterial distributions in the unit partition under the microscope, etc.
On average, there is one stain point per 4 unit area on the plane, observing the number of points on a certain area x,x approximate obedience ()----- Poisson Distribution
here a unit area has a stain point can be regarded as a random event, and in a certain area to observe this certain area can be regarded as unit time
Probability theory related
