Open, activate, and close grahics devices.
(single) number of plot device.
title of the plot device; not yet used.
The number of a graphics device cannot be 0 or 1. The function will work for the operating systems Mac OS, MS Windows, and most Linux systems.
figno is negative and a graphics device with that number does
exist, it will be closed.
No return value, except when a device of that number does not exist, in which case it returns a list of numbers of open graphics devices.
Does not bring the activated graphics device in front.
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