At 17:06 +0100 3/20/08, TSa wrote: >BTW, do we have a unary multiplikative inversion operator? >That is 1/ as prefix or **-1 as postfix? Perhaps .inv as method? >Do we have .neg for additive inversion?
There certainly is the unary minus even though it is badly interpreted in some languages, thankfully NOT including perl 5. Don't even think about parsing = -$x**2; so that it returns a positive result. Perl 5 handles it by assigning a higher precedence to ** than to addition. The real fact is that the minus sign in the above formula just isn't a unary minus in chalkboard algebra. = $a - $b - f($x); when $a is known to by identically equal to $b should be the same as = 0 - f($x); or just = - f($x); which happens easily with pencil and paper. Don't allow it to become = f(-$x); ## wrong! even if the f() is really written as $x**2 or has some other postfix operation - inversion - that's considered a function by a mathematician. ***** At 15:01 +0100 3/20/08, TSa wrote: >BTW, operator overloading does not allow to change the precedence, >associativity and commutativity of the operator because these are >parser features. A vector on the chalkboard can be a row or a column but in a computer it's an ordered list with the vertical or horizontal order of the components residing only in the mind of the programmer. Multiplying a vector by a matrix implicitly indicates that the vector is a row. Multiplying a matrix by a vector implies a column vector and the results are quite different. =$vector * $matrix; is probably well handled in a overloading method because the order implies the rowness or columnness of the vector but it could get confused by a parser that has its own ideas about precedence and commutativity. -- --> From the U S of A, the only socialist country that refuses to admit it. <--
