## 12590 Reputation

8 years, 243 days

## ?...

Your function of Pe also depends on several variables and some arbitrary functions!
How can you imagine that the limit could be computed?

## assume or assuming...

@mmcdara For me, it's not about assume or assuming.
For the same assumptions, assumptions := a>0, b>0, a*b < 1:
assuming
gives the same results.
Also, in Maple 2022, assumptions := a>0, b>0, b < 1/a:
==> all answers are true (But it seems that in 2023, one answer is FAIL !!).

So, everything seems to be about weakness!

## Unfortunately...

@Carl Love  Unfortunately the assume facility is very weak here.

```restart;
# _EnvTry := true;  # useless
assume(a>0, b>0, a*b<1);
is( (1 + sqrt(1-a^2*b^2))/(a*b) >0 ); # FAIL   ?
is( (1 + sqrt(1-a*b))/(a*b) >0 );     # FAIL   ?
is( (1 + sqrt(1-a^2*b^2)) >0 );       # false ??
is( (1 - sqrt(1-a^2*b^2)) >0 );       # false ??
is( (1 - sqrt(1-a*b)) >0 );           # true
is( (1 + sqrt(1-a*b)) >0 );           # true
```

## c1, c2...

@nm The general solution of the ode  y'' + y = 0  is y = c1*sin(x) + c2*cos(x)  but also
y = c1*(2*sin-7*cos(x)) - c2*(sin(x)-3*cos(x)).

## Remarks...

@dharr a) A square complex matrix C has not a square root iff its Jordan form has a Jordan block having dimension > 1 and eigenvalue 0.

b) For C as in the file (40x40), M := evalf[n](MatrixPower(C, 1/2)), eps = Norm(M^2-C)  then:
n=14-->eps=0.003;  n=16-->eps=2e-4;   n=18-->eps=1e-6;  n=25--> eps=2e-13;  n=30-->eps= 2e-15.

## odetest...

Use odetest to check the solution. Yes, it's a bug.

```restart;
ode:=[diff(x(t), t, t) + 2*diff(x(t), t)/sqrt(L*C) + x(t)/(L*C)];
s5 := dsolve(ode, [x(t)]);
odetest(s5, ode);
s6 := dsolve(ode, [x(t)], method = laplace);
odetest(s6, ode);   # bug
```

## Not the same thing...

@Christian Wolinski The problem is that {a>0, b>0, c>0, d>0} is far for being equivalent to {e1>0, e2>0, e3>0, e4>0}.

## G & E...

@tomleslie
G is the centroid of the (inscribed) quadrilateral P1P2P3P4.
E is the Euler center of  the quadrilateral P1P2P3P4  defined as the point in the intersection of the four Euler circles of the triangles P1P2P3, ..., P4P1P2. (E exists!).

Note that OG = (OP1+OP2+OP3+OP4)/4, OE = (OP1+OP2+OP3+OP4)/2,  OPk  being vectors.

## Proof...

@Alex0099  1. The order of summation does not matter, the summand being symmetric.

2. The proof could be very tricky. Probably here the Residue Theorem should be useful.

## restart...

@Thomas Dean  In Windows, after a restart everything is OK. Sorry, I don't use Linux.

## type...

@emendes  procedure is a type, so, its use is covered.

## Draghilev...

AFAIK the Draghilev method is to find a natural parametric representation of a curve given as an intersection of n surfaces in (n+1) unknowns. That is what Rouben did, but using direct computations.

(I was never able to find the original article of Draghilev, but there are many places -- even in this site -- where the method is used).

## first, last...

@lcz Replace:

```first:= fsolve((f(t)-x0)^2+(g(t)-y0)^2=0.02^2, t=0..1);
last := fsolve((f(t)-x3)^2+(g(t)-y3)^2=0.02^2, t=0..1);
```

## @Stretto I don't see how you co...

@Stretto I don't see how you could make ArgK to work. As it is, after correcting the Is problem (see acer's comment), it would work only when computing the values in an array, but not randomly (in any language!). I'd suggest to take the dsolve approach.

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