## 12810 Reputation

8 years, 323 days

## T...

Why not use mtaylor?
Or, the next proc which is even faster:

```T:=(x,y,x0,y0,N) -> eval(series(f(x0+t*x,y0+t*y),t,N),t=1);
```

## generators...

with(GroupTheory):
G := SmallGroup(48, 8);

G :=  < a permutation group on 48 letters with 5 generators >

gen:=NonRedundantGenerators(G);
gen := [(1283)(4122218)(5112117)(614713)(9163120)(10153219)(2336

4744)(24354843)(25344542)(26334641)(27402938)(28393037), (14721

82265)(21114183171312)(923294531472725)(1024304632482826)(1533

394319413735)(1634404420423836), (1910)(21516)(31920)(42324)(5

2526)(62728)(72930)(83132)(113334)(123536)(133738)(143940)(1741

42)(184344)(214546)(224748)]

lprint(gen);
[Perm([[1, 2, 8, 3], [4, 12, 22, 18], [5, 11, 21, 17], [6, 14, 7, 13], [9, 16,
31, 20], [10, 15, 32, 19], [23, 36, 47, 44], [24, 35, 48, 43], [25, 34, 45, 42]
, [26, 33, 46, 41], [27, 40, 29, 38], [28, 39, 30, 37]]), Perm([[1, 4, 7, 21, 8
, 22, 6, 5], [2, 11, 14, 18, 3, 17, 13, 12], [9, 23, 29, 45, 31, 47, 27, 25], [
10, 24, 30, 46, 32, 48, 28, 26], [15, 33, 39, 43, 19, 41, 37, 35], [16, 34, 40,
44, 20, 42, 38, 36]]), Perm([[1, 9, 10], [2, 15, 16], [3, 19, 20], [4, 23, 24],
[5, 25, 26], [6, 27, 28], [7, 29, 30], [8, 31, 32], [11, 33, 34], [12, 35, 36],
[13, 37, 38], [14, 39, 40], [17, 41, 42], [18, 43, 44], [21, 45, 46], [22, 47,
48]])]

nops(gen); # number of generators
3

## database...

It is easy to find the soluble groups using the builtin database:

for n in [60, 120, 168, 180] do SearchSmallGroups( 'order' = n, soluble) od;

Finding a polynomial in Z[X]  for such groups is another problem; I don't think Maple or other CAS can do that efficiently.

## Isomorphic...

C6 is a NOT a subgroup of S5. It is just isomorphic to a subgroup of S5.

1. use e.g.
# or
evala((x^2 - 2)/(x - sqrt(2)));

2. Example:
A := <124,12; "NA/101", ">2.6"; 1,2>:
AA :=map(u -> `if`(type(u,numeric),u,undefined),  A);

## The assume facility...

The assume facility is far from perfect. You can find many examples searching this site.
It is designed for simple conditions; it has evolved in time but with very small steps. At least here, the result (FAIL) is not wrong.

Note also, that the assume facility often ignores the endpoints in inequalities.
Example:
limit(a^n, n=infinity) assuming a>=1;
infinity

limit(a^n, n=infinity) assuming -1 <=a, a<1;
0

## list of generators...

```restart;
with(GroupTheory):
G:=Symm(4);
GroupOrder(G);
do
H := Subgroup([RandomElement(G),RandomElement(G)], G);
C := Core(H, G);
until is(GroupOrder(C) <> 1) and is(GroupOrder(C) <> GroupOrder(H)):
H;
C;
GroupOrder(C) <> GroupOrder(H);
```

```restart;
with(LinearAlgebra): with(plots):
n:=3:
f:=-x^2 + 2*y^2 + 2*z^2 - 6*x + 4*x*y - 4*x*z - 8*y*z + 4*z - 12:
f:=eval(f, [x=x[1],y=x[2],z=x[3]]);
L:=10:
quad:=implicitplot3d(f, x[1]=-L..L, x[2]=-L..L, x[3]=-L..L, style=surface, scaling=constrained):
A:=VectorCalculus:-Hessian(1/2*f,[seq(x[i],i=1..n)]):
b:=eval(Vector( [ seq(diff(f,x[i]),i=1..n)]), [seq(x[i]=0,i=1..n)]):
c:=eval(f,[seq(x[i]=0,i=1..n)]):
X:=Vector([seq(x[i],i=1..n)]):
solve([ seq(diff(f,x[i]),i=1..n)],{seq(x[i],i=1..n)}); # the center
X0:= Vector[column]( eval([seq(x[i],i=1..n)],%) ):
J,Q:=Eigenvectors(A):
T:=Matrix(GramSchmidt([seq( Q[..,j],j=1..n)],normalized)): # T is orthogonal
fnew:=simplify( (T.X+X0)^+. A. (T.X+X0) + b.(T.X+X0) + c ); # ==> Hyperboloid of Two Sheets
col:=[red,yellow,blue]:
ax:=seq(arrow(X0, T[..,j], length=10, width=0.3, color=col[j]), j=1..n):
display(quad, ax, orientation=[175,63,21], caption="Hyperboloid of Two Sheets");
```

## Yes...

```restart;
f := (x,y)->(x^2+y^2)^x: f(0,0):=1:
'D[1]'(f)(0,0) = limit((f(x,0)-f(0,0))/x, x=0);
'D[2]'(f)(0,0) = limit((f(0,x)-f(0,0))/x, x=0);
```

## IdentifySmallGroup...

G:=GroupTheory:-GaloisGroup(x^5 + 20*x + 32, x);
Gal(x^5+20*x+32,x)
IdentifySmallGroup(G);
10, 1

G has been identified as [n,d] = [10,1],  see ?IdentifySmallGroup

To identify it as a human, just access the wiki page  List of small groups - Wikipedia

==> [10,1]  corresponds to the non-abelian group D10 (i.e. D5 with Maple notation).

## maths...

arctan(x,y) = - arctan(-x,y)  implies for x=0 that arctan(0,y) = 0,
but this is false for y<0.
[I have used your swapped notation x <--> y ]

## seq...

Replace fn:=solve(...)  with

`seq(['q'=q, 'x'=solve(V__out/120 = 1/sqrt((-m*x^2 + m + 1)^2 + (q*(x - 1/x))^2), x, useassumptions)], q in Q__s) assuming x::positive;`

## GroupOrder...

Correct syntax:

`GroupOrder(ds[2]);`

The result is of course 5, because it is generated by a cycle of length 5.

## formal or assuming...

```sum(-5*3^(-k-1)*(x-2)^k, k=0..infinity, formal);

# or, say something about the domain
sum(-5*3^(-k-1)*(x-2)^k, k=0..infinity) assuming abs(x-2)<3;

# Note that tha radius of convergence is R=3.
```

5/(x - 5)

5/(x - 5)

## series or not series...

Not all ODEs have series solutions around 0.
To illustrate the problem, let's modify a bit your second ODE.

```ode1:=x^2*diff(diff(y(x),x),x)+x*diff(y(x),x)+y(x) = 0:
dsolve(ode1);
```

y(x) = _C1 sin(ln(x)) + _C2 cos(ln(x))

MultiSeries:-series(sin(ln(x)), x=0);

-sin(ln(1/x))

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