(T / F and explain) An NFA accepts the empty string if and only if its initial state is an end state [on hold]

(T / F and explain) An NFA accepts the empty string if and only if its initial state is an end state.

This question is related to automatons and NFA and DFA. Thank you

unit tests: decoupling of redux reducer tests from the state form

Recently, I have been refactoring the shape of the state in a fairly large redux application, and I have discovered that one of the obstacles to doing so is that the tests for my reducers clearly have a lot of "knowledge" about the "shape" of the state tree.

There are many tests that look like this:

const nextState = reduce(startState, action.doSomething());


So now, when I want to restructure so that the somethingwasdone boolean is stored in state.foo.baz.somethingwasdone, I have to make similar changes in a potentially quite large number of tests.

One thing that I have been wondering is: does it make sense to decouple the evidence of reduction of the state form by using selectors? So:

const nextState = reduce(startState, action.doSomething());

The benefit of this is that, when the shape of your state changes, you just have to change the relevant selectors to match, and potentially you don't have to change your reduction tests at all.

A disadvantage is that, when a reduction test fails, you don't know a priori if that is because there is a problem with the reducer, or a problem with a selector. But this does not seem an expensive disadvantage compared to the advantages.

One thing that stops me is that I never see this pattern in the tutorials, books or documentation of redux.

Am I missing something? Are there other disadvantages that I have not thought about? Is the problem I mentioned above more serious than I thought?

Any advice or comments would be very welcome.

Design: Why can't an angular component update the state store directly, rather than through actions and reducers?


I am discovering the state administration for my first Angular 8 application. I am considering the kiosk of the store library, which simplifies the ngrx / store API.

The kiosk store class has a public method. update(key: K, value: T(K)): void, to directly update the field K of the application status. This method is called from a component.ts, like

onSet(value: string): void {
this.store.update('text', value); }

from an example library.

AFAIK, the standard route to update the status is for an intelligent component to send a Action, with an update of the state inside the store by reducer function. (To be fair, the kiosk is also compatible with this).


Why is the Action / Reducer route preferable to a direct store update from a component? When could the latter be justified?


Suppose the first screens of the application are for user input. The entries in a subsequent screen depend on those of a previous screen, but not vice versa. An intelligent angular component is responsible for a screen. A data structure (ViewModel?) Is defined for each of these components. Each time a screen opens, its smart component is filled from the store using the corresponding data structure.

I would like to store all the entries, including invalid ones, in the store, if the "Previous Screen" is pressed, and only the valid entries, if the "Next Screen" is pressed. Should I do a direct update or send an action from the component?

node.js – the react-dropzone-uploader AVI file is stuck in the "preparing" state

With react-dropzone-uploader configured in this way:

 ( extra.reject ? { color: 'red' } : {} )

The loading of a 250 MB .avi file gets stuck in the "readiness" state. Suggestions?

It works well with mp4 files.

const getUploadParams = meta => ::
  return ::
    url: '/'

quantum mechanics: what is the state of the rule born in axiomatic QM?

While physicists have tried several times and have not been able to derive the Birth Rule (for example: https://arxiv.org/pdf/quant-ph/0409144.pdf). I was wondering what axiomatic quantum mechanics had to say about this. Is it fundamentally impossible to derive the birth Rule or is there hope?

Here is a great discussion link in the same spirit:

I suspect that Lubos Motl was something like the opinion of the measure that should be a separate fundamental axiom. If so, I suspect that it becomes a problem to show that there is no non-redundant axiom when the birth rule is included.

eu – Multiple stays of 3 months in a Member State with freedom of movement

EU laws state that EU citizens have the right to reside (that is, travel) in other member states without restrictions for up to three months.

If I stay in a member state for three months, can I leave for a period of time (say one month) and then have the right to re-enter and stay another month (or three months if necessary)?

Note that this question is no about the Schengen rules.

matrices – State space model / description of the suggested blood ratio and insulin ratio

I am currently trying to solve a state space model for the proportion of blood sugar and the proportion of insulin in a person.

The following is presented in the problem:

I (t) = proportion of insulin in the body

S (t) = proportion of blood sugar in the body

The stable reference state is a fixed level with a suggested blood level = S0 and the insulin level is zero.

The following properties are presented for each state variable (I (t), S (t)):


  1. The presence of insulin increases the suggested turnover (= reduced suggested blood content). The higher the suggested content and insulin, the greater the rotation. It is assumed that the blood level decreases proportionally to the product of sugar and insulin content.
  2. If the blood sugar level falls below the stable reference point (S0). The sugar will be distributed by the liver proportionally to the sugar deficit.
  3. There is an increase in blood sugar when eating food. The effect of this is proportional to the function of time z (t)


  1. If the blood sugar level exceeds S0, insulin is released, proportional to the excess sugar.
  2. Insulin itself has a limited duration. Half of the free insulin becomes inactive in 10-25 min.
  3. If the patient is diabetic, an external injection should be performed. It is assumed that the amount of insulin fed is proportional to a function of w (t), which describes the injection pattern.

The question is:

Provide a description of the state space with the relationship of blood sugar content (S (t)) and insulin content (I (t)) as status variables.

What I have tried / interpreted: for Sugar:

  1. S & # 39; (t) = -k1 (S (t) -S0)
  2. k3 (S0-S (t)) = S (t)
  3. Z (t) = S (t)

combined: S & # 39; (t) = -k1 * k2 * I (t) * S0 + k1 * k2 * I (t) * S (t) – k1 * k2 * I (t) * z (t)

For insulin:

  1. k3 (S0-S (t)) = I & # 39; (t)
  2. k4 (I (t)) = I (t)
  3. w (t) = I (t)

Combined: I & # 39; (t) = k3 (S0-S (t)) + k4 (I (t) + w (t))

Is the interpretation correct? If so, how do I continue to obtain the state space variables S (t) and Y (t)?

Tourism – Can a foreign citizen living in the United States drive with a foreign license outside their home state?

I am a foreign citizen who has been living in the United States for some years. I do not intend to drive in my home state (Maryland), so I have not bothered to convert my foreign license into a US license. UU. However, I want to be able to rent cars for short trips in states other than my home state (California, Colorado, etc.) picking up a rental car at the airport.

Many of the DMV state websites claim that, as a foreign or foreign short-term visitor, you can drive with your foreign or foreign license, but I'm not sure if this strictly applies to the special case of residents of another US state. . UU. Who owns a foreign license.

The few times I tried, I had no problem renting a car, but am I playing with fire when I do this (for example, if I get stopped or if the car is damaged)?

Thank you!

usability: how to resolve the ambiguity of the selected state in a segmented control with only two segments?

I am working on a web application that has two similar data grids on one page. The user should be able to switch between these two data grids within the same page.

I have used segmented buttons to navigate between these two grids. But I feel that this component visually becomes a lever, and the current state of the lever becomes ambiguous.

From now on, I rely solely on the color / tone to show the selected state, but I think it is not clear which state is selected.

Is there a better approach to solve this problem?

Buttons segmented in red circles
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Physical Mathematics – Schrödinger Operators: current state between ballistic movement and the absolutely continuous spectrum?

About Schrödinger operators $ H = Delta + V $ in $ mathbb {R} ^ d $ or $ mathbb {Z} ^ d $, People say that $ H $ it manifests ballistic movement if the square root of the second moment of the position operator grows linearly with time. From what I understand, there are several examples of $ H $ that manifest a ballistic movement and a purely absolutely continuous spectrum, so there is the dogma that one must come with the other; Correct me if this is wrong.

From Barry Simon's proof that the spectrum of pure points implies the absence of ballistic movement (90s), what is the current state of knowledge in the literature?

Does the ballistic movement imply (purely) an absolutely continuous spectrum?

Does the (purely) absolutely continuous spectrum imply ballistic movement?

Are there counterexamples of dogma?

What are the main open questions on this topic?

What are a couple of good references?
Thank you