path of the output file for knit(); if NULL, this
function will try to guess and it will be under the current working
directory
compiler
a character string which gives the LaTeX program used to
compile the tex document to PDF (by default it uses the default setting of
texi2pdf, which is often PDFLaTeX); this argument will
be used to te
envir
the environment in which the code chunks are to be evaluated
(for example, parent.frame(), new.env(), or
globale