Inverse distribution functions: icdf

### 9.4.21 Inverse distribution functions: icdf

The icdf command finds the inverse cumulative distribution function for a probability distribution.

- cdf takes one or more mandatory arguments and one optional argument.
  - distd, the name of the function that finds the distribution’s density function.
  - parameters, any parameters that would normally be passed to distd.
  - x, a number.
- icdf(distd,parameters) returns an expression for the inverse cumulative distribution function for distd with parameters parameters.
- icdf(distd,parameters,x) returns the value of the inverse cumulative distribution function at x. parameters.

Example.
Input:

icdf(normald,0,0.5,0.975)

Output:

0.97998199227