overloading times operator

*To*: mathgroup at smc.vnet.net*Subject*: [mg88820] overloading times operator*From*: gstaples <gstaceystaples at yahoo.com>*Date*: Sat, 17 May 2008 05:32:08 -0400 (EDT)

I wrote a procedure to define the non-commutative product of two elements of the form e_X e_Y, where X and Y are multi-indices. I do this using Times. I do a simple calculation like Expand[(e_{1} + e_{3})(e_{1} - e_{3})] and get the wrong answer. (On the first try.) If I then re-execute the code that defines the multiplication, I repeat the calculation and get correct output. Alternatively, if I execute e=Symbol["e"] before loading the procedure, I get correct output on the first try. More troubling is that after getting correct output, if I perform calculations of a different kind (e.g. matrix multiplication), when I repeat my original calculation, I start getting incorrect output again. (Until I re-execute the code that defines the multiplication.) It's frustrating to repeat a calculation and get different sets of output depending on what other calculations are done in between. Does anyone have suggestions?