On Friday, 96/05/10, Erik Huelsmann wrote to all about "Converting
infix to postf" as follows:

EH> I am looking for some routine that (helps me or does 
EH> itself) converts infix-math-expressions to postfix-math-
EH> expressions.

Hi Erik,

The algorithm is known as the Bauer-Samuelson algorithm. It has been
widely published since the early 1960's. The reference I last used (c.
1974) was "A Compiler Generator" by McKeeman, Horning and Wortman.

EH> If anybody knows a goed book on expression evaluation, I 
EH> would like to know that too. Little problem is the fact 
EH> that I use pascal, but I can read C(++) code.

The above book covers all sorts of stuff like that. The samples are in
McKeeman's language he called XPL. It should be fairly easy for a
Pascal programmer to read, since it is a very trimmed down dialect of
PL/I. [I.e., it's block structured.]

EH> The expression I want to get to work first is:
EH> 
EH>  X*(X'*X)^(-1)*X'*y
EH> 
EH> Yes, it is regression, but don't mind that. I know it has to be
EH> converted to:

As a statistician I recognise the normal equations immediately.
Remember that these are matrices and vectors, and therefore
multiplication is not necessarily commutative. [This algebra is
getting to be a bit of a drag; I've recently posted some similar stuff
on commutative/associative (or not) arithmetic operations in the
C_echo.] Your scope to reorder things is exceedingly limited in a matrix
domain.

Regards

Dave


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