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# cdft_p

Calculates the one-sided probability given a t-value and the degrees of freedom.

## Prototype

```	function cdft_p (
t   : numeric,
df  : numeric
)

return_val  :  numeric
```

## Arguments

t

A scalar or array containing t-values.

df

A scalar or array of the same size as t containing the number of degrees of freedom.

## Return value

A array of the same size as t. Double if any of the input arguments are double, float otherwise.

## Description

Using the cumulative distribution function for the T distribution, calculate the one-sided probability associated with one or more t-values and degrees of freedom. Technically, this is the integral from -infinity to t of the t-density distribution.

The source code is from source routine "CDFT" from DCDFLIB (Double precision Cumulative Distribution Function LIBrary).

## Examples

Example 1

```     t  = 2.12
df = 16

P = cdft_p(-t, df)   ; P = 0.025
P = cdft_p( t, df)   ; P = 0.975
```
Note: the following could be used to calculate the two-sided significance given t and df:
```     prob = betainc( df/(df+t^2), df/2.0, 0.5)    ; prob=0.05   [PROB=1-prob=0.95]
```