## sql server – Signal wait not the same as wait_time_ms for SOS_SCHEDULER_YIELD in sys.dm_os_wait_stats

In short, no.

If you read up on `SOS_SCHEDULER_YIELD`, you’ll see that `SOS_SCHEDULER_YIELD` is not necessarily indicative of CPU pressure.

Several parts of the description listed on that page are quoted here, to help explain. I suggest reading the rest for more/better context.

This wait type is when a thread was able to execute for its full thread quantum (4 milliseconds in all versions of SQL Server, unchangeable), and so voluntarily yielded the scheduler, moving to the bottom of the Runnable Queue in its scheduler.

The most common cause of SOS_SCHEDULER_YIELD waits that I see is queries doing scans of pages that are in memory and aren’t changing, hence there’s no contention for page access and the scanning thread can run until it exhausts its thread quantum.

One more thing to consider is whether your workload is running on a VM that’s experiencing delays because of the host being oversubscribed. This can elevate the number of SOS_SCHEDULER_YIELD waits

## sql server – Difference between signal wait and SOS_SCHEDULER_YIELD

I don’t understand the difference between the signal waits column and SOS_SCHEDULER_YIELD wait type when using sys.dm_os_wait_stats.

Edit: just made a bit more reasearch: it seems that with SOS_SCHEDULER_YIELD we have an exception. But does it then mean that SOS_SCHEDULER_YIELD never has signal waits?

## Is there a good analogy between spectral representation of a signal and graph theory?

I am working on some time series problems where the Fourier representation of the signal in the frequency domain is also important. I am wondering if there is any connection between time series signals consisting of sinusoidal/inherently periodic functions (functions that can be cleanly represented by a sum of sinusoids) and graph theory.

Thanks,
Josiah

## privacy – What is the most basic smartphone that will still run Signal well?

My current phone (S9+) is just not cutting the mustard any more. It’s too big and has too many features I never use. I wanted to switch to a dumb phone but from a security and privacy standpoint, it is not a great option. I am wondering what the most simple smartphone that will run Signal messenger since that is all I ever use my phone for, messaging and calling. I was thinking Nexus 5 but what experience do you have with other phones?

## What should the beep signal signify in fob design?

Fobs typically emit an audible sound, usually a beep, to indicate they have read the key which was swiped. The fob then unlocks if the key swiped was the correct key. Therefore, logically speaking, the beep signal of a fob should indicate that the key has been read by the fob. However, I have found consistently across many fobs that if you swipe the correct key “too fast” the fob will emit the receive key signal, but will not unlock the door.

My question is, what should the beep signal signify to the user? I feel that the beep signal should always, and only, signify reception of the correct key. I see no reason for fobs to beep either for an incorrect key or for an inconclusive swipe. In fact, the crux of my question could be phrased thus: “Should an inconclusive swipe, and a conclusive swipe of the correct key both be signified by the same beep?” I have observed countless times when users hear the beep of a correct key swipe then proceed to open the door only to find it locked and have to swipe again.

## display – External screen is black – no signal – macbook pro 16 2019

display – External screen is black – no signal – macbook pro 16 2019 – Ask Different

## end to end encryption – E2EE verification without meeting in person (in Signal)

I’m playing around with e2ee a little. Would it be possible to verify the security numbers in the signal protocol by using already verified e2ee channels within the app securely?

Let E be a commutative cipher and for a message m donate m_ab as m is encrypted with E in a way that only a and b can decrypt it.
Let a: m -> b denote, that a sends message m to b.

I have four parties A,B,C and S, where S represents the application server.

I have verified E2EE encryption for A&B and for B&C, i want to create it for A&C.

Would the following be secure enough to be used in an application (like Signal)?

1. A&C do a Handshake, but someone could be in the middle (mainly the Server S)

2. A encrypts (a digest of the) sn for C using an authenticated encryption algorithm and the derived key from 1, calling this hsnA

3. A sends hsnA to C via B, this is done as follows:

3.1 A: hsnA_ab -> S

3.2 S: hsnA_ab_ss -> B

3.3 B: hsnA_ss_bc -> S

3.4 S: hsnA_bc -> C

3.5 C decrypts it with the keys he has and compares it to his own digest. If the secrets of A and C match then C can also see that the authTag is valid.

1. C sends a digest of the sn to A in a similar way.

For me this looks like it is sound and correct:

Correctness: If both of them have the same secret this should be secure anyway as hsnA and hsnC are encrypted and only the two of them know how to decrypt it. Neither B nor S can see the message unencrypted at any point in this case.

Soundness:

1. This obviously allows the server to perform a known-plaintext-attack, but this shouldn’t be an issue for modern ciphers if I recall correctly.

2. To me it seems like neither B nor S can change the message that is being sent. They could do so if S=B were the man in the middle, but the clients could choose who they trust to be in the middle on each verification

Is there anything I miss? Why is something like this not already implemented for an easier verification process?

## notifications – Notify when getting “no signal” on the LG Q6

For several days now, the LG Q6 has made me angry when it suddenly stops detecting the SIM card. (once or twice a day)

I don’t want to discuss the cause and possible solution. (Restart always helps)

The worst part is that the outage cannot be predicted.

Therefore, I want to ask if there is any way that would alert me to this. Either in the absence of a SIM card or on the loss of connection (of course, when the airplane mode is not activated).

## differential equations – Asymptotic Output Tracking – Where to Place the Input Control Signal?

Asymptotic Output Tracking: Code Issues

I ask for help from specialists in differential equations, dynamical systems, optimal control and
general control theory;

I have the following system of differential equations:

$$begin{cases} frac{dx(t)}{dt}=G(t) \ frac{dz(t)}{dt}+z(t)=frac{df}{dt} \ frac{dG(t)}{dt}+G(t)=z(t) cdot alpha sin(omega t) \ frac{dH(t)}{dt}+H(t)=z(t) cdot (frac{16}{alpha^2}(sin(omega t)-frac{1}{2})) \ frac{dX(t)}{dt}+X(t)=frac{dx(t)}{dt} end{cases}$$

where, $$x,z,G,H,X$$ – variables; $$f=-(x(t)+alpha sin(omega t)-x_e)^2$$; $$alpha, omega$$ – parameters.

As an output $$y$$, I assign:

$$y=tanh(k cdot H(t))$$

As an reference signal $$r_1$$, I assign:

$$r_1=-1$$

As an constant time $$p_1$$, I assign:

$$p_1=-1$$

Well, I tried to program this in the Mathematica program and ran into a difficulty that I can’t get over yet. Question: in which of the equations should the control signal $$u(t)$$ be placed?

I chose the first equation, then the original system of equations will look like this:

$$begin{cases} frac{dx(t)}{dt}=G(t)+u(t) \ frac{dz(t)}{dt}+z(t)=frac{df}{dt} \ frac{dG(t)}{dt}+G(t)=z(t) cdot alpha sin(omega t) \ frac{dH(t)}{dt}+H(t)=z(t) cdot (frac{16}{alpha^2}(sin(omega t)-frac{1}{2})) \ frac{dX(t)}{dt}+X(t)=frac{dx(t)}{dt} end{cases}$$

(***)

``````Clear("Derivative")

ClearAll("Global`*")

Needs("Parallel`Developer`")

S(t) = (Alpha) Sin((Omega) t)

M(t) = 16/(Alpha)^2 (Sin((Omega) t) - 1/2)

f = -(x(t) + S(t) - xe)^2

Parallelize(
asys = AffineStateSpaceModel({x'(t) == G(t) + u(t),
z'(t) + z(t) == D(f, t), G'(t) + G(t) == z(t) S(t),
H'(t) + H(t) == z(t) M(t),
1/k X'(t) + X(t) == D(x(t), t)}, {{x(t), xs}, {z(t), 0.1}, {G(t),
0}, {H(t), 0}, {X(t), 0}}, {u(t)}, {Tanh(k H(t))}, t) //
Simplify)

pars1 = {Subscript(r, 1) -> -1, Subscript(p, 1) -> -1}

Parallelize(
fb = AsymptoticOutputTracker(asys, {-1}, {-1, -1}) // Simplify)

pars = {xs = -1, xe = 1, (Alpha) = 0.3, (Omega) = 2 Pi*1/2/Pi,
k = 100, (Mu) = 1}

Parallelize(
csys = SystemsModelStateFeedbackConnect(asys, fb) /. pars1 //
Simplify // Chop)

plots = {OutputResponse({csys}, {0, 0}, {t, 0, 1})}
``````

At the end, I get an error.

``````At t == 0.005418556209176463`, step size is effectively zero;
singularity or stiff system suspected
``````

It seems to me that this is due to the fact that either in the system there is a ksk somewhere, or I have put the control input signal in the wrong equation. I need the support of a theorist who can help me choose the right sequence of actions to solve the problem.