poisscdf (Statistics Toolbox)

Poisson cumulative distribution function (cdf)

Syntax

```
P = poisscdf(X,LAMBDA)
```

Description

poisscdf(X,LAMBDA) computes the Poisson cdf at each of the values in X using the corresponding parameters in LAMBDA. Vector or matrix inputs for X and LAMBDA must be the same size. A scalar input is expanded to a constant matrix with the same dimensions as the other input. The parameters in LAMBDA must be positive.

The Poisson cdf is

Examples

For example, consider a Quality Assurance department that performs random tests of individual hard disks. Their policy is to shut down the manufacturing process if an inspector finds more than four bad sectors on a disk. What is the probability of shutting down the process if the mean number of bad sectors () is two?

probability = 1 - poisscdf(4,2)
probability =
    0.0527

About 5% of the time, a normally functioning manufacturing process will produce more than four flaws on a hard disk.

Suppose the average number of flaws () increases to four. What is the probability of finding fewer than five flaws on a hard drive?

probability = poisscdf(4,4)
probability =
    0.6288

This means that this faulty manufacturing process continues to operate after this first inspection almost 63% of the time.

perms poissfit