SetOutputFile — Redirect PHPlot output to a file
$plot->SetOutputFile($output_file)
SetOutputFile arranges for image output to be sent to
a file instead of to the browser (or standard output). By default, output
is sent to the browser (or standard output, if running from the command
line).
The output file will only be produced if SetIsInline(True) is called.
By default, there is no output file, and the image is written to the browser or standard output.