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A general description is here.
The parser now incorporates code from Romain Francois' parser package, to support more detailed computation on the code, such as syntax highlighting, comment-based documentation, etc. Functions ‘getParseData()’ and ‘getParseText()’ access the data.
Many ‘.Call()’ calls in package ‘base’ have been migrated to ‘.Internal()’ calls.
‘solve()’ makes fewer copies, especially when ‘b’ is a vector rather than a matrix.
‘solve(A, b)’ for a vector ‘b’ gave the answer names for ‘colnames(A)’ for ‘LINPACK = TRUE’ but not in the default case.