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| (100344) | |
Re: Canarsie CBTC |
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Posted by Stephen Bauman on Sat Jun 18 11:25:55 2005, in response to Re: Canarsie CBTC, posted by RonInBayside on Sat Jun 18 10:44:55 2005. after 3 secondsYou still need a velocity reading every second. What is the accuracy in ft/sec of each reading taken at 1 second intervals? You may assume that each position reading is accurate to +/- 15 feet and each time reading is accurate to one part in 106. |
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Re: Canarsie CBTC |
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Posted by RonInBayside on Sat Jun 18 11:41:57 2005, in response to Re: Canarsie CBTC, posted by Stephen Bauman on Sat Jun 18 11:25:55 2005. I would venture to say the error would be +/- 23 feet per second at a velocity of 73 feet per second. That is what you really want, is it not?But AIM pointed out my error in assuming that this error rate is cumulative. I compared it in an earlier post to an inertial reference system, where error is cumulative. AIM pointed out that GPS readings are inependent of each other and therefore the error is not additive. (Thank you, Al.) I also noted your objection to AIM's explanation, but I do not fully agree with it. Yes, repeatability is there; but if your measurements are independent of one another, and not dependent on the previous measurement, then that will tend to limit your total error. |
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Re: Canarsie CBTC |
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Posted by Stephen Bauman on Sat Jun 18 12:15:56 2005, in response to Re: Canarsie CBTC, posted by RonInBayside on Sat Jun 18 11:41:57 2005. I would venture to say the error would be +/- 23 feet per second at a velocity of 73 feet per second.That answer is not correct. Hint, the magnitude of the error is independent of the velocity travelled. For simplification, you may assume that the time measurement is completely accurate. Again, 1 reading every second. |
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(Sponsored) |
iPhone 6 (4.7 Inch) Premium PU Leather Wallet Case - Red w/ Floral Interior - by Notch-It |
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Re: Canarsie CBTC to Jeff |
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Posted by Terrapin Station on Sat Jun 18 22:04:42 2005, in response to Re: Canarsie CBTC to Jeff, posted by Brother Pielet on Sat Jun 18 07:08:55 2005. I'm not sure what type of GPS Terripan STation usesI use a Magellan SporTrak Map GPS receiver. It's great. Whenever the train I'm on hits the speed limit and holds there, my receiver always reports the correct speed. So I know it is accurate. |
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Re: Canarsie CBTC |
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Posted by Broadway Junction on Sat Jun 18 22:09:43 2005, in response to Re: Canarsie CBTC, posted by RonInBayside on Sat Jun 18 10:46:59 2005. dumbass |
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| (100513) | |
Re: Canarsie CBTC to Jeff |
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Posted by Brother Pielet on Sat Jun 18 23:28:06 2005, in response to Re: Canarsie CBTC to Jeff, posted by Terrapin Station on Sat Jun 18 22:04:42 2005. IIRC during the debate we had over these devices several months ago, your accuracy stated for that machine was of plus or minus 10 feet. As far as GPS is concerned, I wouldn't put trust in them at all if they are that far off but they do navigate just fine. If a device can not compute feet per second accurately then it isn't accurate. |
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| (100532) | |
Re: Canarsie CBTC to Jeff |
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Posted by tracksionmotor on Sun Jun 19 00:53:36 2005, in response to Re: Canarsie CBTC to Jeff, posted by Terrapin Station on Sat Jun 18 22:04:42 2005. Look up LORAN A and LORAN C and then come back to me. Since theinnacuracy protocol was dropped for maritime safety (55 minutes of the hour for civillian usage with a rotating position indication) the GPS is better BUT it still is poor timing in the city and not fast enough for CBTS...doesn't work underground too. I don't get lost often...just stuck in traffic, I have a $175 earned credit with Verizon for a new contract phone...my old one was purchased just before 911. CI peter |
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| (100562) | |
Re: Canarsie CBTC |
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Posted by Jeff H. on Sun Jun 19 03:37:10 2005, in response to Re: Canarsie CBTC, posted by RonInBayside on Sat Jun 18 08:27:55 2005. Oh, so you don't have any inside information from Siemens?OK, it's a draw then. I apologize for mis-interpreting your post. When you made oblique references to "a certain French vendor" sending you express mail packages with information, I thought you meant Siemens (although Siemens is a German company, it is the France division which has the contract for CBTC). |
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Re: Canarsie CBTC / GPS |
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Posted by Jeff H. on Sun Jun 19 03:43:36 2005, in response to Re: Canarsie CBTC, posted by Stephen Bauman on Sat Jun 18 09:42:30 2005. I don't know how this tangent about using GPS got started, becauseno one that I can think of is using it for railway signaling or thinking about it. BUT, as long as we're on the subject: Did you forget one important thing about the GPS system? It is a service provided by the US military, and can be withdrawn at any time without notice. Wasn't it turned off for a while after Sep 11 (or maybe that was just selective availability)? |
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Re: Welcome to 2nd grade |
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Posted by Jeff H. on Sun Jun 19 03:51:59 2005, in response to Re: Welcome to 2nd grade, posted by RonInBayside on Sat Jun 18 09:15:05 2005. You're right, Ron, HS Relay has very little knowledge ofthe emergency repairs at Chambers St. :) Whew, it's a good thing the D line was recently upgraded, otherwise the TA would have had no spares. |
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Re: _three_ manufacturers |
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Posted by Jeff H. on Sun Jun 19 03:55:40 2005, in response to _three_ manufacturers, posted by H.S.Relay on Sat Jun 18 08:17:28 2005. I skipped Alstom as a domestic manufacturer because of the waythey absorbed GRS. Alcatel's got US&S, but they pretty much let it stand as an independent business unit. GRS has been swallowed whole. Can you even get a "K" relay from them anymore? You can from SAFETRAN. |
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Re: Canarsie CBTC |
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Posted by AlM on Sun Jun 19 06:20:40 2005, in response to Re: Canarsie CBTC, posted by Stephen Bauman on Sat Jun 18 11:21:25 2005. Still, do you have any evidence that GPS measurement errors are NOT strongly correlated in both space and time? My understanding is that they are, but if I am wrong I would like to know.I am asking out of genuine curiosity; nothing whatsoever to do with use of GPS for subway trains. |
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Re: Canarsie CBTC |
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Posted by AlM on Sun Jun 19 06:43:34 2005, in response to Re: Canarsie CBTC, posted by Stephen Bauman on Sat Jun 18 12:15:56 2005. Hint, the magnitude of the error is independent of the velocity travelled. For simplification, you may assume that the time measurement is completely accurate.You are asking a fiendishly difficult question here. Let me state it as a probability problem. X is a vector-valued random variable with expected value (0,0,0). Let D(X) be the random variable = |X-(0,0,0)|. We are given that D(X) has a normal distribution, an expected value of 0, and variance 15x15=225. Y is a vector-valued random variable with expected value (D1,0,0). Let D1(Y) be the random variable = |Y-(D1,0,0)|. D1(Y) has a normal distribution, an expected value of 0, and variance 15x15=225. X and Y are independent. What is the standard deviation (i.e., square root of the variance) of the random variable |X-Y|? If this were all in one diminesion, you could assume that the variance of the difference of two independent normally distrbuted random variables is the sum of the variances, and the standard deviation would be 15 x SQRT(2). But it's not all in one dimension, which makes the problem very difficult. I have taught basic college level probability but don't even want to think about the integrals you'd have to do to calculate that answer. |
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| (100576) | |
Re: Canarsie CBTC / GPS |
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Posted by RonInBayside on Sun Jun 19 08:04:45 2005, in response to Re: Canarsie CBTC / GPS, posted by Jeff H. on Sun Jun 19 03:43:36 2005. "Did you forget one important thing about the GPS system? It isa service provided by the US military, and can be withdrawn at any time without notice." True statement. However, the military in the US reports to civiolian leadership, and shutting down GPS access to the civilian world is not something the military would do (even if some general talks about it publicly) without extensively consulting with the White House and Congress. There are too many people with a stake in this to allow such a shut-off to actually happen. In general "can do x without notice" very rarely translates into "will do x without notice," and business people who make decisions about GPS do not worry too much about this. If it ever came up the next attack on Washington would be the Army of Lobbyists crossing the Potomac. There's no known defense for that. 8-) "Wasn't it turned off for a while after Sep 11 (or maybe that was just selective availability)? " There might have been some action taken, but it was limited and short-lived. If you look at the bigger picture, turning off GPS would cost this country a lot more than the attack itself did. There is a parallel in aviation. There were calls from members of Congress after 9/11 to completely ground general aviation in this country for an extended period. If you weren't a military pilot or you weren't an airline captain, you weren't getting off the ground in any way shape or form. And of course Reagan Airport closed down for a while and there was talk of permanently closing it. Both ideas were shot down, thankfully. |
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| (100577) | |
Re: I'd like proff. |
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Posted by H.S.Relay on Sun Jun 19 08:08:32 2005, in response to Re: I'd like proff., posted by RonInBayside on Sat Jun 18 09:07:50 2005. -So You can't. okay. |
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| (100578) | |
Re: _three_ manufacturers |
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Posted by H.S.Relay on Sun Jun 19 08:09:49 2005, in response to Re: _three_ manufacturers, posted by Jeff H. on Sun Jun 19 03:55:40 2005. Ansaldo has the Switch, Not Alcatel. The Alcatel partner on Bergen is Safetran. |
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| (100580) | |
Re: Canarsie CBTC |
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Posted by RonInBayside on Sun Jun 19 08:11:56 2005, in response to Re: Canarsie CBTC, posted by Jeff H. on Sun Jun 19 03:37:10 2005. "Oh, so you don't have any inside information from Siemens?"I repeatedly told you I didn't. "OK, it's a draw then." No it isn't. We all lose. You lost a chance to lear something and correct some serious misininformation you have about CBTC in general, risk and safety issues (which you are dead wrtong about) and to be able to check your assertions about Siemen's CBTC scheme against the company's information. But you refused to do that. So I have to do it. Over the next couple of weeks I'll try to find some email addresses or postal addresses to write to Siemens. Time permitting I'll send an inquiry and post the answers here. It would have been better if you did it. |
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| (100581) | |
Re: _three_ manufacturers |
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Posted by BIE on Sun Jun 19 08:17:20 2005, in response to Re: _three_ manufacturers, posted by Jeff H. on Sun Jun 19 03:55:40 2005. "K" Relays? HELL, Even I am in the process of switching to GRS/ Alstom type B's for the control of signals on my model railroad. |
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| (100585) | |
Re: I'd like proff. |
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Posted by RonInBayside on Sun Jun 19 08:22:47 2005, in response to Re: I'd like proff., posted by H.S.Relay on Sun Jun 19 08:08:32 2005. "Be objective and inclusive, and don't opinionate"Why not opinionate. My opinion , well founded, is that people who make specific assertions about a technology should be able to at least discuss the specifics. If they can't, iit calls their assertions into question. If the person happens to be educationally qualified in EE or electronics, an additional opportunity during discourse is lost. |
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| (100586) | |
who is john galt? |
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Posted by H.S.Relay on Sun Jun 19 08:24:19 2005, in response to Re: Welcome to 2nd grade, posted by RonInBayside on Sat Jun 18 09:15:05 2005. "The TA doesn't know how many man-hours it will..."How do you know the TA doesn't know how do it? Read for comprehension. The TA has no experience in THE AMOUNT OF TIME it will take to make this repair. Siemens told you but didn't tell them?" I'm sorry, who am I, exactly? Recall that the emergency repair program they did was enabled by using spares that were taken off the D line and fortunately were still available. I don't recall doing that. -but hey, you're the medical consultant, not me. |
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| (100590) | |
Re: Canarsie CBTC |
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Posted by H.S.Relay on Sun Jun 19 08:35:19 2005, in response to Re: Canarsie CBTC, posted by RonInBayside on Sat Jun 18 08:49:39 2005. Which department? The French guys who used to be "Matra."This is not the proper forum to post technical specifications for a safety-critical system. Jeff's synopsis is about as detailed as one would want to get. It might be easy for me to prove you wrong, if you listed any points you disagreed with. If you're not going to post details then why should anyone? |
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| (100595) | |
Re: Canarsie CBTC |
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Posted by RonInBayside on Sun Jun 19 08:58:19 2005, in response to Re: Canarsie CBTC, posted by H.S.Relay on Sun Jun 19 08:35:19 2005. "This is not the proper forum to post technical specifications for a safety-critical system."False statement. It's an appropriate forum to discuss just about anything technical relating to rail. If you don't want to discuss it, you find a nice cop-out like that. "Jeff's synopsis is about as detailed as one would want to get." Also false. |
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| (100597) | |
Re: Canarsie CBTC |
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Posted by Stephen Bauman on Sun Jun 19 09:02:21 2005, in response to Re: Canarsie CBTC, posted by AlM on Sun Jun 19 06:43:34 2005. You are asking a fiendishly difficult question here.I do not think so. Perhaps, that is why Mr. Bayside has not yet responded. Let me restate something to make it a little clearer. I am asking for the accuracy, not the error. The accuracy is the maximum value of the error. Let me state it as a probability problem. X is a vector-valued random variable with expected value (0,0,0).... I think you are reading too much into the question I posed. But it's not all in one dimension, which makes the problem very difficult. I have taught basic college level probability but don't even want to think about the integrals you'd have to do to calculate that answer. The usual way for dealing with vectors, is to assume that all the vector components are independent gaussian random variables. Any rotation or translation of the axes means that the vectors will have independent gaussian random variables, when expressed in the new coordinates. Similarly a translation to polar coordinates results the radius length being a rayleigh random variable and the angle being a uniform random variable with both being independent of one another. |
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Re: Canarsie CBTC |
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Posted by RonInBayside on Sun Jun 19 09:34:02 2005, in response to Re: Canarsie CBTC, posted by Stephen Bauman on Sun Jun 19 09:02:21 2005. "Perhaps, that is why Mr. Bayside has not yet responded."Mr. Bayside does occasionally have to do other things, like take his wife out to dinner, brush his teeth and so on. And this morning I have to water my baby trees before the height of the day. But I am enjoying this part of the thread. I always enjoy your discourses on math. Happy Father's Day to you, Stephen, by the way. |
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Re: who is john galt? |
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Posted by BIE on Sun Jun 19 11:24:52 2005, in response to who is john galt?, posted by H.S.Relay on Sun Jun 19 08:24:19 2005. John Galt is a fictional character in a trashy little piece of filth called Atlas Shrugged written by the soft core porn writer, ayn rand. it is the Right's answer to mein Kampf and the communist manifesto. |
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Re: who is john galt? |
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Posted by I Know Jack on Sun Jun 19 11:38:11 2005, in response to Re: who is john galt?, posted by BIE on Sun Jun 19 11:24:52 2005. What does who John Galt is or was have to do with CBTC? |
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Re: who is john galt? |
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Posted by BIE on Sun Jun 19 11:44:21 2005, in response to Re: who is john galt?, posted by I Know Jack on Sun Jun 19 11:38:11 2005. I don't know, H.S. Relay asked. |
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Re: who is john galt? |
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Posted by Chris R16/R2730 on Sun Jun 19 12:38:18 2005, in response to Re: who is john galt?, posted by BIE on Sun Jun 19 11:24:52 2005. You have both misconceptions and issues with Ayn Rand as well as the political right. |
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Re: _three_ manufacturers |
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Posted by Jeff H. on Mon Jun 20 02:48:55 2005, in response to Re: _three_ manufacturers, posted by H.S.Relay on Sun Jun 19 08:09:49 2005. Crap, three foreign signal vendors which begin with "A"...I alwaysmake that mistake. Kinda like the power walker with the white curly hair...is he Roger or Ron? |
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Re: _three_ manufacturers |
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Posted by Jeff H. on Mon Jun 20 02:50:10 2005, in response to Re: _three_ manufacturers, posted by BIE on Sun Jun 19 08:17:20 2005. Are you using them for effect? There are certainly more compactnon-vital relays that will do the same thing (they don't quite scale 1:80). |
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Re: Canarsie CBTC |
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Posted by AlM on Mon Jun 20 12:39:28 2005, in response to Re: Canarsie CBTC, posted by Stephen Bauman on Sun Jun 19 09:02:21 2005. OK, the maximum value of the error is a much simpler problem. |
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Re: Canarsie CBTC |
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Posted by Stephen Bauman on Mon Jun 20 22:08:56 2005, in response to Re: Canarsie CBTC, posted by AlM on Mon Jun 20 12:39:28 2005. the maximum value of the error is a much simpler problem.Mr. Bayside still has more important things to do than try to solve the problem. His solution thus far has been for a government demonstration project. |
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Re: Canarsie CBTC |
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Posted by tracksionmotor on Mon Jun 20 22:18:19 2005, in response to Re: Canarsie CBTC, posted by Stephen Bauman on Mon Jun 20 22:08:56 2005. Herr Doktor Baumann...this is......forgive me.....bullshit. |
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Re: Canarsie CBTC |
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Posted by RonInBayside on Mon Jun 20 23:51:36 2005, in response to Re: Canarsie CBTC, posted by Stephen Bauman on Mon Jun 20 22:08:56 2005. "His solution thus far has been for a government demonstration project."I already know that government works. It is you who wants the government to shut down completely. 8-) |
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Re: Canarsie CBTC |
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Posted by RonInBayside on Mon Jun 20 23:59:10 2005, in response to Re: Canarsie CBTC, posted by Stephen Bauman on Sat Jun 18 12:15:56 2005. OK, so assuming one independent measurement each second, the maximum error in each measurement is + or - 15 feet. It remains +/- 15 feet each time it is measured regardless of velocity.So the maximum error after 1 second is 15 feet; after 2 seconds it is 15+15=30 feet; after 3 seconds 30+15 feet = 45 feet. It is t*(max error of one measurement). I am adding nothing for velocity, but I am assuming that the error occurs only along one axis (the track). |
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Re: Canarsie CBTC |
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Posted by Stephen Bauman on Tue Jun 21 05:15:40 2005, in response to Re: Canarsie CBTC, posted by RonInBayside on Mon Jun 20 23:59:10 2005. I am adding nothing for velocity, but I am assuming that the error occurs only along one axis (the track).The question was and remains: what is the accuracy of the velocity estimation given that the accuracy for each position measurement is +/- 15 feet and that velocity estimates are required every second? You may assume that over the 1 second interval that the track is straight. |
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Re: Canarsie CBTC |
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Posted by RonInBayside on Tue Jun 21 09:54:50 2005, in response to Re: Canarsie CBTC, posted by Stephen Bauman on Tue Jun 21 05:15:40 2005. Thank you. I'd lost track of your actual question. Let d = distance between intervals.So if the position error is 0 at t0, 15 feet at t1, 30 feet at t2, 45 feet at t3 (where we talk about 1 second intervals): The velocity estimate at t1 is accurate within +/- 15 feet per second; the velocity at time t2 is (d(t1:t2) +/- 15 feet)/ 1 second The velocity estimate at time t3 is (d(t2:t3) +/- 15 feet) / 1 second . So the estimate of velocity at each of the intervals will vary at most by + or - 15 feet per second. |
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Re: Canarsie CBTC |
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Posted by Stephen Bauman on Tue Jun 21 11:28:52 2005, in response to Re: Canarsie CBTC, posted by RonInBayside on Tue Jun 21 09:54:50 2005. the estimate of velocity at each of the intervals will vary at most by + or - 15 feet per second.No. That's overly optimistic by half. |
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Re: Canarsie CBTC |
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Posted by RonInBayside on Tue Jun 21 12:10:17 2005, in response to Re: Canarsie CBTC, posted by Stephen Bauman on Tue Jun 21 11:28:52 2005. So you are saying the velocity estimate will be accurate to at most 30 feet per second.I see my error now. An error in one direction of 15 feet followed by another in the opposite direction produces an error of 30 feet. Thank you. |
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Re: Canarsie CBTC |
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Posted by Stephen Bauman on Tue Jun 21 12:26:42 2005, in response to Re: Canarsie CBTC, posted by RonInBayside on Tue Jun 21 12:10:17 2005. the velocity estimate will be accurate to at most 30 feet per second.Do you suppose that a technology that can estimate the velocity to an accuracy of 30 ft/sec (20 mph) is appropriate for a CBTC? |
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Re: Canarsie CBTC |
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Posted by RonInBayside on Tue Jun 21 12:40:09 2005, in response to Re: Canarsie CBTC, posted by Stephen Bauman on Tue Jun 21 12:26:42 2005. Yes it is, depending on the circumstances. In a transit operation with trains close together, no. In a commuter rail operation with trains once per hour, why not? You can periodically "zero" the error using wayside equipment (and use less of it due to CBTC's presence).And what makes you believe GPS won't improve over the next 5 years? Suppose the accuracy improves to 15 feet per second (10 mph)? Would that change its usefulness? By the way, thank you for engaging me in the math exercise. If you ever decide to write a textbook (you should!) I would like to have an autographed copy. |
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Re: Canarsie CBTC |
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Posted by Stephen Bauman on Tue Jun 21 13:10:50 2005, in response to Re: Canarsie CBTC, posted by RonInBayside on Tue Jun 21 12:40:09 2005. In a commuter rail operation with trains once per hour, why not?How accurate does the position data have to be for ATO? Consider the following. Trains are composed of 10 cars, each 60 feet long. Each car has 4 doors on each side that are equally spaced along the length of the car. Each door is approximately 4 feet wide. The station platforms are 600 feet long. |
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| (101539) | |
Re: Canarsie CBTC |
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Posted by RonInBayside on Tue Jun 21 13:21:05 2005, in response to Re: Canarsie CBTC, posted by Stephen Bauman on Tue Jun 21 13:10:50 2005. I see what you are getting at. I considered in my previous post the need for trains to be separated from each other. Improvements in GPS will help that.Your question regarding stations is a good one. I would say that currently and in the immediate future at least, wayside equipment at the station would be necessary to assure the train's proper and safe arrival. Suppose we had a 10 mph- accurate GPS. Take a stretch of track three miles long between stations. It seems to me that we could be able to operate a commuter rail service there with GPS beteen thestations but wayside equipment at the stations. |
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Re: Canarsie CBTC |
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Posted by Stephen Bauman on Tue Jun 21 13:25:39 2005, in response to Re: Canarsie CBTC, posted by RonInBayside on Tue Jun 21 13:21:05 2005. Suppose we had a 10 mph- accurate GPS. Take a stretch of track three miles long between stations. It seems to me that we could be able to operate a commuter rail service there with GPS beteen thestations but wayside equipment at the stations.Is there a curve with a speed restriction between those stations? |
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Re: Canarsie CBTC |
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Posted by RonInBayside on Tue Jun 21 13:33:38 2005, in response to Re: Canarsie CBTC, posted by Stephen Bauman on Tue Jun 21 13:25:39 2005. I assumed for the example that it was straight track to keep it consistent with your question to me.But a curve and speed restriction present an interest question. The travel is still basically on a vector -the track. The train will not depart from the track most of the time (we hope!) The train would have to know when it is entering the restricted speed zone. This might be a problem because of the increase in maximum position error (15 feet per second). So if the curve close enough to the departure station so that GPS' error is not ecessive, you don't nee wayside equipoment there. Further away from a threshold we agree upon, you'd need wayside equipment. |
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Re: Canarsie CBTC |
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Posted by Stephen Bauman on Tue Jun 21 13:38:49 2005, in response to Re: Canarsie CBTC, posted by RonInBayside on Tue Jun 21 13:33:38 2005. Further away from a threshold we agree upon, you'd need wayside equipment.Wasn't CBTC supposed to get rid of inaccessible wayside equipment? That was how it was supposed to save maintenance costs, remember? |
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Re: Canarsie CBTC |
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Posted by RonInBayside on Tue Jun 21 13:47:57 2005, in response to Re: Canarsie CBTC, posted by Stephen Bauman on Tue Jun 21 13:38:49 2005. "Wasn't CBTC supposed to get rid of inaccessible wayside equipment?"If GPS (which is what we are discussing) could cut the requirement for wayside equipment by two-thirds but not eliminate it, isn't that a substantial savings? We were discussing GPS and its application to CBTC. CBTC offers substantial savings without even considering GPS. |
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Re: Canarsie CBTC |
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Posted by Stephen Bauman on Tue Jun 21 18:38:56 2005, in response to Re: Canarsie CBTC, posted by RonInBayside on Tue Jun 21 13:47:57 2005. If GPS (which is what we are discussing) could cut the requirement for wayside equipment by two-thirds but not eliminate it, isn't that a substantial savings?Compared to what? Do nothing? Use different technology for estimating instantaneous velocity and position? |
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Re: Canarsie CBTC |
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Posted by RonInBayside on Tue Jun 21 18:42:52 2005, in response to Re: Canarsie CBTC, posted by Stephen Bauman on Tue Jun 21 18:38:56 2005. Compared to current conventional relay-based fixed block signaling. In other words the "No Build" alternative (so yes, in effect "do nothing") |
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Re: Canarsie CBTC |
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Posted by Stephen Bauman on Tue Jun 21 20:42:49 2005, in response to Re: Canarsie CBTC, posted by RonInBayside on Tue Jun 21 18:42:52 2005. In other words the "No Build" alternative (so yes, in effect "do nothing")There are other alternatives. |
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