Wikipedia:Reference desk/Archives/Computing/2014 October 17

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October 17

Spam filters and Gmail

The organization that I do tech support for has an email account that forwards everything it gets to six people. Two of those people are complaining about a high amount of spam coming to them daily (100+ messages) through that address. My wife is one of the recipients. She uses Gmail and says that she only gets 5-10 spam emails a day and most of those don't come via this specific address. Is it possible that Gmail is filtering out most of the spam before it even gets to her and lands in her spam box? I wouldn't think that they would do that just in case of any false positives but I'm sort of grasping at straws here as to why only two of the people are complaining about the amount of spam they receive. Thanks, Dismas|^(talk) 00:56, 17 October 2014 (UTC)

By default Gmail (and a lot of other providers) filter what they suspect to be spam into a spam folder and don't forward it to the inbox or via POP3.--Phil Holmes (talk) 08:06, 17 October 2014 (UTC)

Yes, I realize that. I guess I wasn't clear. What I mean is, does Gmail not even show some stuff in the spam box? Is it so confident that some of it is spam that it just deletes it without the user ever knowing it was sent to them? Dismas|^(talk) 13:24, 17 October 2014 (UTC)

I suppose it's possible that Google blacklists certain specific servers that it knows to be 100% spam, preventing them from ever delivering the email, but my intuition is that it would not refuse do such a thing to forwarded email. I could be wrong. 75.140.88.172 (talk) 02:08, 19 October 2014 (UTC)

There are fair number of internet blacklists; server list (for want of a better name), which a lot of companies and individuals use as a source of known spam servers referenced by IP/Domain. Heres an example http://www.spamhaus.org/sbl/ Sirrob01 (talk) 04:11, 22 October 2014 (UTC)

PyEvolve vs. DEAP vs....?

Hi all! We are trying to breed some parameter configurations controlling the search of a deduction system. Some parameters are integers, some are reals, some are boolean, and the most complex one is a variable length list of different elements, where each of the elements has its own (smallish) sub-set of parameters. Since we have Python competence and Python is already used in the project, that looks like a good fit. I've found DEAP (software) and PyEvolve as already existing frameworks for genetic algorithms. Does anybody have experience with these and can tell me about the strengths and weaknesses of the two (or any other appropriate) systems? If it helps: In our application, determining the fitness of the individual is likely the most expensive part - it will certainly be minutes per generation, and if we are not careful and/or rich, could be hours per individual ;-). So time taken by the rest of the GA is probably not a major factor - think "several generations per day", not "several generations per second". --Stephan Schulz (talk) 07:39, 17 October 2014 (UTC)

Given the project description, it might be worth spending a small amount of time considering other techniques, such as stochastic hill climbing or simulated annealing, if you haven't already. SemanticMantis (talk) 15:09, 17 October 2014 (UTC)

Thanks for the suggestions. I've basically been doing manual GAs with some local hill-climbing for the last 15 years, so I have a strong intuition that GAs might work well in this domain. There already is some related work trying other techniques. --Stephan Schulz (talk) 16:29, 17 October 2014 (UTC)

لیلا — Preceding unsigned comment added by 37.254.31.90 (talk) 17:02, 17 October 2014 (UTC)

Laptop start up and use speed

Are laptop speeds faster when it's plugged in on both start up and during use? Why if so? — Preceding unsigned comment added by 92.27.141.165 (talk) 19:16, 17 October 2014 (UTC)

I assume you meant plugged in to an electrical outlet. If so, I wouldn't think there should be a speed diff. There are various actions possibly taken to conserve energy while running on batteries, like dimming the screen, but I don't think any of those would slow things down. It is conceivable that they could run the CPU at a lower speed to limit heat production and required fan usage, but that seems rather like driving slowly to conserve gasoline when running low. (It's true it will use gas more slowly, but it won't get you to the gas station before gas runs out. Similarly, a slow laptop won't finish a task on a given charge which a fast laptop won't.) StuRat (talk) 22:42, 17 October 2014 (UTC)

The above answer is wrong. Power consumption grows superlinearly with clock rate, so reducing the clock rate reduces the total energy cost of a computation.

Whether a laptop is slower when unplugged depends on OS power settings. By default it probably will be somewhat slower, but you can change that if you don't like it. -- BenRG (talk) 08:02, 18 October 2014 (UTC)

Do some laptops really have an option to reduce the clock rate while running on batteries ? Mine doesn't. StuRat (talk) 15:03, 18 October 2014 (UTC)

The Terminal in Macs can seemingly do anything. But I don't know about that. I'd guess so. If I run Windows or DOS in a shell, I can change the speed, but not sure if that's just an emulator illusion. InedibleHulk (talk) 15:23, 18 October 2014 (UTC)

On Windows laptops you can change power schemes from the Power Options control panel. To see or change the CPU throttling, click "Change plan settings" then "Change advanced power settings" and look under "Processor power management". SpeedStep has more information (this is an Intel trademark, but I think AMD is very similar). Other hardware, like the GPU and the hard drive, may also support slower low-power modes. -- BenRG (talk) 03:59, 19 October 2014 (UTC)

... and Stu is partially wrong about the car, too. As I'm sure he knows, driving conservatively (gentle acceleration and minimal braking) does save fuel, and fuel consumption grows superlinearly with speed, at least it does above about 50 mph. Dbfirs 11:41, 18 October 2014 (UTC)

I was talking about driving slowly, not accelerating slowly. And 50 mph isn't what I would call "slow", 25 mph is. At such low speeds gasoline powered cars are less efficient. StuRat (talk) 15:07, 18 October 2014 (UTC)

Efficiency depends on engine speed rather than road speed. I notice very little difference in fuel consumption between 25mph and 50 mph, but consumption tends to rise (efficiency falls) for speeds outside this range, but I accept your explanation. Dbfirs 21:35, 18 October 2014 (UTC)

Since the relevant efficiency is clearly miles per gallon, then the road speed most certainly figures into it. (A car may well idle longer on a given amount of gas, but it certainly won't get more miles per gallon while idling.) And if you mean a car could be geared differently so it has another optimal cruising speed, that certainly is true, but manufacturers will pretty much always optimize their cars for highway speeds (with a possible exception for commuter vehicles meant only for use in cities). StuRat (talk) 22:01, 18 October 2014 (UTC)

Yes, we're talking about different, but related efficiencies. Below 25mph the mpg drops because more of the power of the engine is lost in gearing down and heat loss. Above 50mph the mpg drops because of air resistance. In between these speeds, the two effects roughly cancel out (depending on the car design and gearing). Most engines are designed to run at maximum efficiency at between 1500 and 2500 rpm.

Windows laptops usually have a "Power Plan" configuration that adjusts clock rate according to preferences between maximum performance speed and maximum processing per battery charge. Dbfirs 22:26, 18 October 2014 (UTC)