Algorithms – Solve / mitigate the problem of the free pilot without requiring identification?

Is there an algorithm / protocol to solve / mitigate the problem of the free pilot without requiring identification?

In a web system, I want to distribute exactly one virtual dollar per day to each person, without the need for identification when people create an account.

A mitigation solution would mean, for example, that a person can get up to $ 2 per day (in case he has created more than one account), but not much more.

I also need a solution that distributes to each person approximately the same amount of money per day. Then, the ratio between the money distributed to every two different people per day should be around 1.

What are the benefits of the static website?

Hello friends,

What are the benefits of the static website?

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nginx: another PDO could not find the driver problem

I have been working for the last two nights to configure my own LEMP server on Amazon ec2. I am not a server expert, so it has been slow, and the last error "The driver could not be found" appears when I try to create the new PDO object.

I have read what dozens of threads look like about this error, and unfortunately none of the solutions seem to work for me. For the most part, everyone says I have to install php-mysql, but of course that is not available:

$ sudo yum install php-mysql
Last metadata expiration check: 0:22:54 ago on Sat 17 Aug 2019 02:26:41 AM UTC.
No match for argument: php-mysql
Error: Unable to find a match

Meanwhile, phpinfo () seems to report that a driver is installed ??

MySQL driver for PDO    George Schlossnagle, Wez Furlong, Ilia Alshanetsky, Johannes Schlueter

But In the PDO section of phpinfo () it says:

PDO drivers     odbc, sqlite

So, I guess the mysql driver is really missing? Leaving me in the same place, finding it and installing it … But how to find the right one for my configuration? I tried using yum to search but that failed (big surprise):

$ yum search php-
Red Hat Update Infrastructure 3 Client Configuration Server 8                                                                   0.0  B/s |   0  B     00:00
Error: Failed to synchronize cache for repo 'rhui-client-config-server-8'

Google search that error made me lose myself in hundreds of other threads, none of which helped …

Can anyone point me in the right direction? I imagine that there is a simple command that I need to execute that is particular to my configuration, I just need to find out what it is …

Some other things I've tried:

  • run a php script from the Linux command prompt to verify that the problem
    it exists there: it does
  • check the php.ini settings (they look good, I'll paste them next)
  • check the configuration of /etc/php-fpm.d/www.conf (these also look good, they will be pasted below)

Here are my various operating system details:

$ cat /etc/os-release
NAME="Red Hat Enterprise Linux"
VERSION="8.0 (Ootpa)"
ID="rhel"
ID_LIKE="fedora"
VERSION_ID="8.0"
PLATFORM_ID="platform:el8"
PRETTY_NAME="Red Hat Enterprise Linux 8.0 (Ootpa)"
ANSI_COLOR="0;31"
CPE_NAME="cpe:/o:redhat:enterprise_linux:8.0:GA"
HOME_URL="https://www.redhat.com/"
BUG_REPORT_URL="https://bugzilla.redhat.com/"
REDHAT_BUGZILLA_PRODUCT="Red Hat Enterprise Linux 8"
REDHAT_BUGZILLA_PRODUCT_VERSION=8.0
REDHAT_SUPPORT_PRODUCT="Red Hat Enterprise Linux"
REDHAT_SUPPORT_PRODUCT_VERSION="8.0"

$ php -v
PHP 7.2.11 (cli) (built: Oct  9 2018 15:09:36) ( NTS )
Copyright (c) 1997-2018 The PHP Group
Zend Engine v3.2.0, Copyright (c) 1998-2018 Zend Technologies

$ nginx -v
nginx version: nginx/1.14.1

$ mysql --version
mysql  Ver 8.0.17 for Linux on x86_64 (Source distribution)

and some excerpts from php.ini:

(Pdo)
; Whether to pool ODBC connections. Can be one of "strict", "relaxed" or "off"
; http://php.net/pdo-odbc.connection-pooling
;pdo_odbc.connection_pooling=strict

;pdo_odbc.db2_instance_name

(Pdo_mysql)
; If mysqlnd is used: Number of cache slots for the internal result set cache
; http://php.net/pdo_mysql.cache_size
pdo_mysql.cache_size = 2000

; Default socket name for local MySQL connects.  If empty, uses the built-in
; MySQL defaults.
; http://php.net/pdo_mysql.default-socket
pdo_mysql.default_socket=

Excerpts from /etc/php-fpm.d/www.conf:

user = nginx
group = nginx

I hope that's enough information – thanks in advance for any help!

differential equations: problem when combining ParametricNDSolve with NonlinearModelFit

I am finding some inconsistencies in making NonlinearModelFit work with the ParametricNDSolve output. Here is an example that works (starting with a new Kernel):

eqs = {a'(t) == -k1 a(t) - k2 a(t)^2, 
       b'(t) == k1 a(t) + k2 a(t)^2, 
       a(0) == a0, b(0) == b0};
fixedparams = {k1 -> 1.2, b0 -> 0};
fns = {a, b};
params = {k2, a0};
solution = ParametricNDSolve(eqs /. fixedparams, fns, {t, 0, 5}, params)
fitfn = a /. solution;
paramsForDataSet = {k2 -> 1.263, a0 -> 0.0321};
dataset = {#, ((fitfn @@ params) /. paramsForDataSet)(#) + 
  RandomVariate(NormalDistribution(0, 0.0002))} & /@ Range(0, 5, 0.01);
ListPlot(dataset, PlotRange -> Full)

enter the description of the image here

initialGuess = {k2 -> 2.0, a0 -> 0.3};
tmp = Values@initialGuess;
Dynamic@Column({Show(ListPlot(dataset, PlotRange -> Full), 
                     Plot((fitfn @@ tmp)(t), {t, 0, 5}, 
                          PlotRange -> Full, PlotStyle -> Red), 
                  PlotRange -> Full, ImageSize -> Large), 
                ListPlot({#1, #2 - (fitfn @@ tmp)(#1)} & @@@ dataset, 
                         PlotRange -> Full, AspectRatio -> 0.2, 
                         ImageSize -> Large)})

This last bit gives me a graph of dynamic updating of my adjustment and waste as it converges. Here is the adjustment procedure:

result = NonlinearModelFit(dataset, (fitfn @@ params)(t), 
                       Evaluate(List @@@ initialGuess), t, 
                       StepMonitor :> (tmp = params))
tmp = Values@result("BestFitParameters")

enter the description of the image here

enter the description of the image here

This looks great! But when I complicate the model a bit, I drop the core. Again from a new core:

eqs = {a'(t) == -k1 a(t) - k2 a(t)^2, b'(t) == k1 a(t) + k2 a(t)^2, 
       c(t) == q a(t) + r b(t), c(0) == q a0 + r b0, a(0) == a0, 
       b(0) == b0};
fixedparams = {k1 -> 1.2, b0 -> 0};
fns = {a, b, c};
params = {k2, a0, q, r};
solution = ParametricNDSolve(eqs /. fixedparams, fns, {t, 0, 5}, params)
fitfn = c /. solution;
paramsForDataSet = {k2 -> 1.263, a0 -> 0.0321, q -> 0.341, 
                    r -> 0.8431};
dataset = {#, ((fitfn @@ params) /. paramsForDataSet)(#) + 
       RandomVariate(NormalDistribution(0, 0.0002))} & /@ Range(0, 5, 0.01);
ListPlot(dataset, PlotRange -> Full)

enter the description of the image here

initialGuess = {k2 -> 2.0, a0 -> 0.3, q -> 0.32, r -> 0.88};
tmp = Values@initialGuess;
Dynamic@Column({Show(ListPlot(dataset, PlotRange -> Full), 
                     Plot((fitfn @@ tmp)(t), {t, 0, 5}, PlotRange -> Full, 
                     PlotStyle -> Red), 
                  PlotRange -> Full, ImageSize -> Large), 
                ListPlot({#1, #2 - (fitfn @@ tmp)(#1)} & @@@ dataset, 
                  PlotRange -> Full, AspectRatio -> 0.2, 
                  ImageSize -> Large)})
result = NonlinearModelFit(dataset, (fitfn @@ params)(t), 
           Evaluate(List @@@ initialGuess), t, 
           StepMonitor :> (tmp = params))
tmp = Values@result("BestFitParameters")

The only differences are:

  • adding c (t) and c (0) to the equations
  • adding c to fns
  • Add q and r to the parameters
  • Add values ​​for q and r to paramsForDataSet and initialGuess
  • changing fitfn to c instead of a

Everything else is identical, but this time the core fails. Any suggestions would be welcome.

(In case this is a mistake in Mathematica, I have sent an error report to Wolfram. However, I do not want to rule out that I may be doing something wrong, so I am also asking here).

forms – Search box design problem

I have two similar types of searches:

  • Customers: can be searched by code, name, state (active or inactive) and zone.
  • Companies: can be searched by code, name and area.

The customer zone and the business zone have different types of information (for example, the customer zone must be a country and the business zones a region)
The results of both searches have the same data structure, so they can be displayed in the same data grid.

I designed this design with tabs, but it doesn't convince me. The code and name are shared in two ways, but the zone combo has different elements. It would be good to find some way to unite them in a unique way.

enter the description of the image here

Graph theory: For what applications of the street vendor problem, is it really important to visit each city at most?

Traditionally, the problem of the street vendor makes you visit a city at least once Y at most once.

However, if you were a true street vendor, you would like the lowest cost route to visit each city at least once, and you would not bother to visit a city 2, 3 or more times. For a given city, you can stop and sell your products only once, and on subsequent visits, just drive around the city without stopping.

Consider an unguided graphic that has an incident city exactly at two edges. The cost on one of these edges is only 10 units, while the cost on the other is 99,999,999,999. If you insist on visiting each city at most Once, then he is forced to incur the cost of the high cost advantage. However, if you allow yourself to visit the cities several times, you simply abandon the way you entered (at the low cost edge). The low cost advantage takes you back to a city that has gone before.

The problem of the street vendor is highly designed for a real street vendor. I want to give students an application for which there is a real incentive to visit each city at most once. For what applications visiting each city is a critical aspect of the problem?

nt.number theory – Propose, evoke or provide a draft to establish a new problem about periods in the spirit of the period definition due to Kontsevich and Zagier

I know from an informative point of view that the notion / definition of what a period due to Kontsevich and Zagier, see (1) or (2). In this MathOveflow, questions were asked about these periods, but I know Mathematics Stack Exchange publications, since those questions are easier for me to understand.

I am curious to know what new problems may arise as open problems related to periods. I prefer questions similar to / in the spirit of (3) or (4), for example: 1) under what conditions for $ f (n) $ is $ sum_ {n = 1} ^ infty f (n) / n ^ s $ a period ($ Re s> 1 $)? (I don't know if this problem has a good mathematical content or if it is in the literature), or questions similar to (3) for same / different operations involving well-known periods. In that case, if this question is interesting, feel free to add a proposal, even if it is beyond my understanding, it sure is interesting for your colleagues on this site.

Question. Evoke by providing details or a draft of what may be good proposals for new open problems over periods. Thank you.

If this question is interesting and has good acceptance or activity, do not hesitate to add the most appropriate labels.

References

(1) Kontsevich and Zagier, Periods, Institut des Hautes Γ‰tudes Scientifiques (2001).

(2) Stefan MΓΌller-Stach, What is … a period?, AMS Notices, Volume 61, Number 8 (September 2014).

(3) Is $ pi / e $ a period?, by Mathematics Stack Schange (October, 2018)

(4) Following the definition of Kontsevich and Zagier, is it known if it is conjectural? $ 1 / zeta (2 million) $, with $ m geq 2 $ An integer must be a point?, from Mathematics Stack Exchange (April 2017).

Huawei Y7 network problem

This happened suddenly and I'm sure nothing happened to the device before that. Now you don't read the SIM cards of the phone. Both incoming and outgoing calls and even text messages are blocked. Show a small cross where the signal bars used to be.

Any method to fix this?

I already tried to reset it. But the problem remains the same.

Algorithms: Can anyone provide proof of the second equation of the rod cutting problem in section 15.1 of the CLRS?

While going through the CLRS DP rod cutting problem, I noticed that the optimal structure of the rod cutting problem is:

π‘Ÿπ‘— = max {𝑝𝑛, π‘Ÿ1 + π‘Ÿπ‘˜ – 1, π‘Ÿ2 + π‘Ÿπ‘— – 2, …, π‘Ÿπ‘— – 1 + π‘Ÿ1}

In the general approach, after the initial cut, each subpart of the rod is considered an independent problem statement, which makes sense since we do not know which will give the optimal solution. But the change occurs after 15.1 is transformed to 15.2, which is:

π‘Ÿπ‘› = max1≀𝑖≀𝑛 {𝑝𝑖 + π‘Ÿπ‘› – 𝑖}

After the first cut, let's take a case of (p3 + r4) Since r4 will return the maximum income after more cuts (if necessary), the first part, that is, p3 of length 3 is not touched here. What if that length of 3 would produce a maximum income when cut to length 2 and 1?

I hope to find an explanation here. PS: Sorry for the syntax of the equations. I don't know MathJax well and I'm too interested in finding an answer to this. Cheers!

text prediction – problem maker when I write an email or username

When I want to write an email or username, or when I search for topics, p. In the stack overflow, when I start writing, I immediately see on the screen things that I wrote in the past and sometimes, even though I write something else, the previous types replace them. It appears when I write to buy on Amazon or when I want to buy a plane ticket, when I want to write labels on a stack overflow site.

How can I neutralize this "help" …?