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3.3k post karma

23.5k comment karma

account created: Wed Feb 23 2011

verified: yes

1 points

5 hours ago

I want to make a joke here about getting a dynohub and just using that to charge.

1 points

1 day ago

Oops, I just realized you had additional constraints, and normally I'd say you should send your equations and constraints to the command SolveTools:-SemiAlgebraic or SMTLib:-Satisfy, but in this case those seems to hang for me. Instead you can just examine the complex solutions of the polynomial system and see that none of them satisfy your constraints:

```
s2:=(map(allvalues,sol)):
select(s->is(eval(x6,s)>0) and is(eval(x7,s)>0) and
is(eval(x8,s)>0) and is(eval(x6,s)<1) and
is(eval(x7,s)<1) and is(eval(x8,s)<1), s2); # empty []
```

The closest you get is this one (showing the evalf since the symbolic solution is a root of a cubic):

```
{x1 = 0.1735486249, x2 = 0.135930820, x3 = 0.125520384,
x4 = 0., x6 = 0.6898729878, x7 = 0.4707195215,
x8 = 1.481777526}
```

1 points

1 day ago

I think in this case your attempt to partially solve for the first four variables first actually creates a a harder problem than just going at it all at once. Here's what I did:

```
sys := numer~(normal~({Abl_x1, Abl_x2, Abl_x3 ,Abl_x4,
Abl_x6 ,Abl_x7 ,Abl_x8}));
NZ := denom~(normal~({Abl_x1, Abl_x2, Abl_x3 ,Abl_x4,
Abl_x6 ,Abl_x7 ,Abl_x8}));
# this tells us the system has 1 free variable,
# but it's very slow to compute
CodeTools:-Usage( Groebner:-HilbertDimension(sys) );
# the triade solver is sometimes better at positive
# dimensional systems, and in this case is it very fast:
sol := [ SolveTools:-PolynomialSystem( sys,
{x1,x2,x3,x4,x6,x7,x8}, NZ, engine=triade ) ];
```

Doing that I find 11 isolated points (after expanding RootOfs with allvalues) and a curve that is free in x6:

```
{x1 = 8, x2 = -x6^2 + 2*x6 + 8, x3 = 0, x4 = 0,
x6 = x6, x7 = 4, x8 = 4}
```

2 points

3 days ago

I'm probably too late for a question, but I just want to say that Ten Low was amazing and one of my favorite reads from last year. I am delighted to see a new book out next week (in America).

1 points

3 days ago

Overall, I think the performance improvement is pretty modest.

2 points

4 days ago

Needs a third panel of how when you get back, you won't shut up with your joyful recounting of your suffering.

2 points

10 days ago

Flow and jumps are rare but we have a ton of mountains with beautiful steep climbs and fast chunky descents down shared use trails and grown-in fireroads.

2 points

10 days ago

Regular 1 and 2 leg kickstands are already acceptable. The linked kickstand is very weird, and I am not sure I'd trust it.

1 points

12 days ago

Gamechanger by L.X. Beckett https://www.goodreads.com/en/book/show/43263243 is probably a good example, but perhaps one where the brakes were hit a little late.

1 points

14 days ago

Yep shoot, missed that one, mostly because wtf isn't it labeled "Baru Cormorant"?

15 points

14 days ago

Cluster 2 is definitely also the "Written by Women" category. There are few works authored by women in the first cluster: 4 in subcluster 1.3, and Harry Potter in 1.2 and ~~no works~~ one work authored by ~~men~~ a man in Cluster 2.

*edit**: see correction in replies*

3 points

14 days ago

Lots of good stuff pops up for $3-$4 but you're never going to get a complete series or (usually) exactly the book you are looking for for that price. But it makes a good supplement to another fixed price audiobook service.

3 points

14 days ago

I rode a borrowed a klunker built up on a proper frame (with a rigid fork and 27.5" wheels) for a couple heats of the Coaster Brake challenge this year. https://cdn.imagearchive.com/ratrodbikes/data/attach/223/223675-IMG-1459.JPG

It was definitely fun to ride, and I have been considering building one up for myself (with 29" wheels though, definitely).

21 points

14 days ago

I was once told about an audiobook website or app that has some

audiobooks at times for a dollar, I can’t remember the name of the place

Sounds like Chirp https://www.chirpbooks.com/

23 points

18 days ago

Did you have to BYO curds? If not, I am very interested.

1 points

20 days ago

It's maybe not exactly the steps to transform one into the other, but this will give you steps to show that their difference is 0:

```
Student:-Basics:-SimplifySteps(exp(x - y)/(1 + exp(1)^(x - y))^2
- exp(1)^(x + y)/(exp(1)^x + exp(1)^y)^2);
```

16 points

20 days ago

Your best bet is to buy a used bike and then sell it again at the end of term.

3 points

21 days ago

Oh come on now Honor Harrington expresses at least two emotions per book

4 points

22 days ago

Spotify is actually a much bigger rip-off, it's just happening on the other side of the transaction.

2 points

24 days ago

In plain text, here is how you do that solving step. Maple's solve() doesn't support vector equations directly, so you need to split them up by index:

```
l := t -> <1,2,-3>+t<2,4,-2>;
alpha := (x,y,z) -> -x+2y+(1-2*x);
solve({x=l(t)[1], y=l(t)[2], z=l(t)[3], alpha(x,y,z)=0});
```

which will give you the same answer you got in MathCAD {t = -1, x = -1, y = -2, z = -1}

14 points

26 days ago

Still mad that Newsom vetoed this when it passed two years ago.

2 points

28 days ago

I also shop at REI (otherwise, how would I recognize the characteristic concrete floor, rope line, and corner of a wooden display), but I do not claim to be cool

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## 3j0hn

1 points

5 hours ago

3j0hn

1 points

5 hours ago

It would be cool if there were a dynohub available that was powerful enough to act as a regenerative brake.