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A general description is here.
R now provides a syntax for specifying raw character constants similar to the one used in C++: ‘r"(...)"’ with ‘...’ any character sequence, except that it must not contain the closing sequence ‘)"’. This makes in easier to write strings that contain backslashes or both single and double quotes. For more details see ‘?Quotes’.
‘mle()’ in the ‘stats4’ package has had its interface extended so that arguments to the negative log-likelihood function can be one or more vectors, with similar conventions applying to bounds, start values, and parameter values to be kept fixed. NB: This has required a minor extension to class ‘"mle"’, so saved objects from earlier versions may need to be recomputed.