## Alec Mihailovs

Dr. Aleksandrs Mihailovs

## 4455 Reputation

19 years, 191 days
Mihailovs, Inc.
Owner, President, and CEO
Tyngsboro, Massachusetts, United States

## Social Networks and Content at Maplesoft.com

I received my Ph.D. from the University of Pennsylvania in 1998 and I have been teaching since then at SUNY Oneonta for 1 year, at Shepherd University for 5 years, at Tennessee Tech for 2 years, at Lane College for 1 year, and this year I taught at the University of Massachusetts Lowell. My research interests include Representation Theory and Combinatorics.

## A very long syllable...

?subgrel page contains an interesting error example with a very short syllable c. It looks more interesting with other syllables,

subgrel({y=[a,b,averylongsyllable]},
grelgroup({a,b}, {[a,a], [b,a]}));

Error, (in subgrel) generator [a, b, averylongsyllable]
contains a syllable `averylongsyllable' that is not a generator,
or the inverse of a generator, of the parent group

Alec

## kernelopts(toolboxdir)...

kernelopts(toolboxdir) crashes mserver both in Classic and Standard Maple 12 on Windows Vista (I didn't check the command line).

Alec

## Differential forms implementation...

I just looked how differential forms are implemented and was quite surprized

with(DifferentialGeometry):
DGsetup([x,y,z],M):
a:=evalDG(dx &wedge dy+2*dy &wedge dz):
lprint(a);

_DG([["form", M, 2], [[[1, 2], 1], [[2, 3], 2]]])

It is an unevaluated function with nested lists as arguments.

Probably, not the worst possible choice since I can imagine few choices that would be worse - strings, for instance. But there are so many other choices that seem much better - antisymmetric Arrays, or tables, for instance. Why lists?

Alec

## Zero in DifferentialGeometry...

Multiplication by 0 gives 0 for differential forms, which is wrong. For example,

with(DifferentialGeometry):
DGsetup([x,y],M):
a:=dx &wedge dy:
3*a;
3 dx ^ dy
0*a;
0

It should be 0 dx^dy.

That reminds me of an old Matrix bug with M^0 being 1 instead of the identity Matrix for square Matrices.

Alec

## Evalapply for Matrices...

I just noticed that usual parentheses work as square brackets for Matrices,

M:=Matrix(2,[a,b,c,d]);

[a    b]
M := [      ]
[c    d]
M(1,2)=M[1,2];
b = b