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`
`**Calling Sequences:**

`rtime`()

`rtime`(*expr*`)
`

**Parameters:**

`
`**Returns:** `real`

`
`**Synopsis:** This function returns the total CPU time taken to
evaluate the expression *expr*`. When no expression is passed, it
returns the number of second since ``00:00:00 GMT, January 1, 1970`.

`
`**Examples:**

> rtime(log10(factorial(100)));

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`

*Gaston Gonnet*

*1998-09-15*