MathGroup Archive 2005

[Date Index] [Thread Index] [Author Index]

Search the Archive

Re: EUREKA Re: Types in Mathematica, a practical example

  • To: mathgroup at
  • Subject: [mg63220] Re: EUREKA Re: Types in Mathematica, a practical example
  • From: David Bailey <dave at>
  • Date: Mon, 19 Dec 2005 07:01:21 -0500 (EST)
  • Organization: Customer of PlusNet plc (
  • References: <do0le4$41j$>
  • Sender: owner-wri-mathgroup at


If you want to compute with undefined array elements, why not use 
subscript elements such as Subscript[a,1,2].

More generally, the concept of a matrix can mean a number of different 

1)	A fully filled rectangular array of numbers or other expressions. 
(SparseArray is simply a variant of this).

2)	An array in which some or all of the elements are undefined.

3)	An array in which even the dimensions are undefined, but in which you 
can refer to individual elements.

4)	In some work a single symbol is used to represent a matrix together 
with a non-commutative multiplication.

Clearly a system cannot be expected to cater for all of these and all 
possible transitions between one and another. In practice, of course, 
Mathematica caters for case 1, and you have to supply your own notation 
to work with the others. This seems reasonable to me.

In practice, I find that error messages generated by Part are quite 
common and extremely useful, and I think it would be most unhelpful if 
Part expressions that could not be evaluated silently returned unchanged.

David Bailey

  • Prev by Date: Re: Uninstall Mathematica v4
  • Next by Date: Re: Re: Output a list of keywords
  • Previous by thread: Re: Imposing boundary condition at infinity
  • Next by thread: NDSolve