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Lean Algorithmic Trading Engine by QuantConnect (Python, C#)
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QUESTION
I went through a lengthy process removing mod_ssl and replaced it with gnutls because I wanted to use TLS 1.3.
The difference I’ve noticed is gnutls doesn’t support older, legacy methods, only new ones.
OpenSSL supports them all. Is that a better choice? I could find very little support configuring with gnutls and Apache other than the RTFM pages.
Cons pro? Should I move back to mod_ssl? I'm leaning towards, I made a mistake with GnuTLS just for TLS 1.3 and to get a good security ranking score.
...ANSWER
Answered 2022-Mar-22 at 03:56Most people use OpenSSL, and it has been updated to work with newer versions of TLS as well as older versions (backwards compatibility).
As far as which is better, I don't know, but most use OpenSSL.
And regarding "Server Fault" in the comment, the user could have been more informative, and likely was referring to the domain, serverfault.com, which they did not elaborate to, making it confusing.
QUESTION
I have a simple interface setter:
...ANSWER
Answered 2021-Dec-16 at 18:57You probably want something like this
QUESTION
I am trying to increment the number in MongoDB using mongoose. But I start failing right at the query stage. When I // @ts-ignore
it flows silently with no error but the value doesn't update.
The error it throws out is: Type 'number' is not assignable to type 'undefined'
My Schema:
...ANSWER
Answered 2021-Dec-10 at 20:05items
is not an array, it is an object. You should access it with items.amount
and NOT with items.$.amount
. Change your query like this:
QUESTION
I have a pretty basic construction of loops in mind for lean. I construct a class for magmata, a class for quasigroups (cancellative magmata), and a class for unital magmata. From there a loop is just something that is both a quasigroup and a unital magma.
In Haskell this would look like
...ANSWER
Answered 2021-Dec-06 at 15:02On Lean 3.35.1, you have several possible solutions. For Haskell-like record merging, there is old_structure_cmd
:
QUESTION
The lidR package has a neat way to work with huge (pointcloud) datasets: The catalog
function (doc here) avoids loading the dataset to memory and can treat mosaics [datasets that are spread across multiple (non-overlapping) tiles] as single dataset. It loads required tiles on-the-fly during computations in an intelligent way. It is great to avoid working with huge files (multiple GBs) and keep memory requirements lean if only working with small parts of the dataset.
Is there a similar convenient/memory-efficient/"lidR-catalog-way" to process large raster mosaics in R? Or more put in a more general way: Is there a way to work with mosaic raster datasets in R without merging them first?
I am aware of the mosaic
(doc) and merge
functions, which allow me to merge my tiled raster mosaic into a single raster dataset. I also found that gdal
will do so a lot faster and memory efficient. Here is a R-snippet for this:
ANSWER
Answered 2021-Nov-30 at 16:52You should look into the terra
package which provides exactly the functionality you're looking for through virtual raster tiles (VRTs). We can use them to treat a collection of raster files on disk as a single raster file while taking advantage of the API to do a majority of the same tasks as you can do through the raster
package.
First, let's create a sample of 4 rasters using the example straight from the ?terra::vrt()
documentation.
QUESTION
I've noticed React Router DOM (v6) is now using functions in their help guides in regards to pages instead of using classes.
Previously used classes like so:
...ANSWER
Answered 2021-Nov-18 at 06:01Class vs Function components is irrelevant in RRDv6, they simply render React components specified as JSX, not as a reference to a component, and not as a function returning JSX. There is also no render
or component
props, the Route
components now use only element
to render the route components.
QUESTION
Symbolic calculations performed manually or by a computer algebra system may be faulty or hold only subject to certain assumptions. A classical example is sqrt(x^2) == x
which is not true in general but it does hold if x
is real and non-negative.
Are there examples where proof assistants/checkers such as Coq, Isabelle, HOL, Metamath, or others are used to certify correctness of symbolic calculations? In particular, I am interested in calculus and linear algebra examples such as solving definite or indefinite integrals, differential equations, and matrix equations.
Update: To be more concrete, it would be interesting to know whether there are examples of undergraduate assignments in calculus and linear algebra that could be formally solved (possibly with the help of a proof assistant) such that the solution can be automatically verified by a proof checker. A very simple example assignment for Lean is here.
...ANSWER
Answered 2021-Nov-15 at 17:54The only thing that comes to my mind is that Isabelle/HOL can replay SMT proofs (as produced e.g. by Z3 or CVC4), e.g. involving integer and real arithmetic. For computer algebra systems, I don't know of any comparable examples.
The problem is that computer algebra systems tend not to be set up in a way where they can output a detailed certificate for their simplifications – if they were able to do that, one could attempt to replay that in a theorem prover. But it would have to go beyond purely equational reasoning, since many rules (such as your example) require proving inequalities as preconditions.
If computer algebra systems were able to output a trace of their computations as a list of rewrite rules that were used, including how to prove each of their preconditions, one could in principle replay such a trace in a theorem prover – but that would of course require that every rule used by the CAS has a corresponding rule in the theorem prover (this is roughly how replaying SMT proofs works in Isabelle). However, I do not know of any projects like this.
There are, on the other hand, various examples where CASs are used to compute some easily verifiable (but hard to compute) result, e.g. factoring a polynomial, isolating the roots of a real polynomial, Wilf–Zeilberger witnesses, and then verifying that this is really a valid result in a theorem prover. However, this does not involve certifying the computation process of the CAS, just the result.
QUESTION
Since around 2 weeks ago, my console filter starts to filter out even matching text. Tried restarting, is currently on the latest chrome version, also tried to restore settings, nothing. Searched on the web too didn't really find anything similar... I am banging my head against the wall right now if anyone has a lead, please... (Apparently one of my coworkers also starts to have this issue recently... )
Edit1: So played with a couple versions of chrome more. I am current on 95.0.4638.69. Tried beta version 96.x, same issue. Tried chromium 94.x, it works all fine! Haven't got a chance to try chrome 94.x as I dont' want to uninstall my chrome yet. But yeah I am leaning towards that the 95.x updates may break it, though I haven't seen any official info regarding it.
...ANSWER
Answered 2021-Nov-09 at 15:27Same issue on Chrome 95.0.4638.69 (latest as of 9 Nov 2021)
Workaround I'm using at present is to use Regular Expression
format in place of standard filter string e.g. test
-> /test/
, then it works just the same
QUESTION
In lean, there exists a notation for the summation sign (Σ
, large Sigma) to write sums with many terms. Sadly, neither the mathlib documentation nor the reference manual seem to provide much information about how it can be used.
What imports are required in order to use it, and how do you write sums with it?
For example, how would you write the theorem that the first n
natural numbers add up to n * (n + 1) / 2
, using the summation sign?
ANSWER
Answered 2021-Oct-23 at 15:34This notation is defined in algebra.big_operators.basic. Here is a minimal working example:
QUESTION
When using the cases
-tactic on an inductive data type, lean produces multiple cases, but does not create a hypothesis stating the assumption of the current case. For example:
ANSWER
Answered 2021-Oct-22 at 20:14Use cases h : c
to get a new hypothesis h
for each case. For more detail, see the documentation.
In the example, this would be
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