Can you still math? - Page 1
Forum section: electronics / general

author: Sparks
author_rank: Contributor
timestamp: March 05, 2015, 04:39:35 pm
content: There I am, sitting in my first college math class, and it hits me... I haven't used more than a few engineering formulas in the past decade.Back in high school math came natural, but now it's like ...whaaaaat?I was just wondering if anyone else out there has had a similar problem

author: IanB
author_rank: Super Contributor
timestamp: March 05, 2015, 04:52:05 pm
content: Use it or lose it?I don't have that problem with math, but I'm sure there are other high school subjects I have forgotten all about by now.

author: codeboy2k
author_rank: Super Contributor
timestamp: March 05, 2015, 04:55:32 pm
content: Quote from: IanB on March 05, 2015, 04:52:05 pmI've forgotten some of the most basic things... like some of the harder matrix maths and some differentiation and integration rules that I used to know by memory..These days I mostly use formulas and solvers and other purpose made software, that I don't do as much math as I used to.I've also taken to reviewing my math skills and refreshing myself using the MIT open courses (and others, such as Coursera) as well as self-paced using the Khan Academy.

author: Ericho
author_rank: Regular Contributor
timestamp: March 05, 2015, 05:19:56 pm
content: Its not a problem, I forgot most stuff I never used again.Now when I need it, pic up a book or watch a YouTube lesson and its back in no time.Can still help the kids with their homework and math problems, just need a day advance warning to pic up on the subject again.You don't use it, you don't loose it, you just hide it in a dark corner of your brian; a small effort brings it back in the light ;-)

author: SeanB
author_rank: Super Contributor
timestamp: March 05, 2015, 05:59:49 pm
content: Step away from the calculator, pull out a pencil and paper and do a few dozen things by hand on paper again. Helps a lot to keep you in practise. I tend to do shopping with a running total maintained either with a shopping list and a pen to write prices down or carry a running total in my head. That at least gives me a good idea of what I am spending, instead of just seeing a figure up on a screen for a second then putting in a card. Knowing what things costs ( and being able to work out per unit prices so you can see the large pack may actually be more expensive per unit) and doing the basic math in your head is good practise.

author: Mechanical Menace
author_rank: Super Contributor
timestamp: March 05, 2015, 06:02:35 pm
content: I can't do anything more than a guestimate without a calculator nowadays, but I was never any good at mental arithmetic anyway.

author: IanB
author_rank: Super Contributor
timestamp: March 05, 2015, 06:04:37 pm
content: I think mental arithmetic isn't mathematics, but it is good practice for mental agility and mental agility helps with mathematics and learning in general.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: March 05, 2015, 11:15:00 pm
content: I keep algebra and calculus fresh. Nothing terribly complex (I wouldn't know where to go if you brought up some quantum mechanics..) but it's useful.Tim

author: Neganur
author_rank: Unknown
timestamp: March 06, 2015, 06:16:44 am
content: if you don't remember fast enough or have trouble grasping new stuff, be sure to grab the course book and get some practise. Also, do team up with someone else as it's a pain in the arse to get stuck on something and have no one to discuss it.

author: miguelvp
author_rank: Super Contributor
timestamp: March 06, 2015, 06:23:58 am
content: https://www.khanacademy.org/It's free and they have all you need to bring up your math to the level that is required for your class, or at least it will help you remembering what you forgot or didn't pay much attention to.Start with Algebra, then vectors and matrices and of course Calculus

author: EEVblog
author_rank: Unknown
timestamp: March 06, 2015, 06:42:26 am
content: Nope.As I've said many times, I haven't solved an integral in 20+ years in the industry, I couldn't do it now to save my life

author: Rerouter
author_rank: Super Contributor
timestamp: March 06, 2015, 07:10:21 am
content: Not much more than algebra, i can still do long addition, multiplication, division with a bit of paper, i have had to start dipping into matrix's and such with no prior knowledge of them, just to try and solve something in software that people only seem to solve using them... (it annoyed the buggery out of me)i'm still fairly fresh but i'm only 2 years out of TAFE, so that may have something to do with it,

author: ConKbot
author_rank: Super Contributor
timestamp: March 06, 2015, 07:31:17 am
content: Been doing school part time while working full time. Got though calc3, and then took a few engineering and physics courses... Now 3 years later, taking differential equations...Bad planning

author: JohnnyBerg
author_rank: Frequent Contributor
timestamp: March 06, 2015, 08:10:42 am
content: I have a son, doing his master. He keeps me sharpAll the knowledge is still there, buried deep.

author: Artlav
author_rank: Frequent Contributor
timestamp: March 06, 2015, 08:44:11 am
content: I tend to do simple arithmetics in my head, just not to lose the skill.For more complex math i tend at least to know what to look for, enough to be able to understand math-laden scientific papers.At worst i can grind through it... But if someone got me to pass any of the old exams google-free, i would likely fail completely.Curious thing is, i can tell which day of the week a certain date of the current year is, after a second of thinking.For some reason that skill stuck, even though i rarely ever use it.

author: Howardlong
author_rank: Super Contributor
timestamp: March 06, 2015, 09:18:05 am
content: Definitely there is value to being able to know whether a number "looks right" both in terms of a bit of rough calculation by looking at the figures and in terms of the experience of knowing when something feels right.When I did maths, there was a joke that if the answer wasn't a fraction of pi then you probably had the wrong answer. That is true to some extent in the exam room, but in engineering it's generally rubbish, and to this day I am not sure of the value of presenting stock questions that have been manipulated to give a particular answer.I very rarely need to resort to solving differential equations, to such an extent where I don't see the point of keeping current. The last time I did anything serious in calculus was 20 years ago, and it ended up that, after several days of head scratching, it wasn't solvable analytically anyway so I used numerical methods.I do, however, work on DSP quite a bit and so complex algebra and trig stuff switching in and out of Euler format is quite common. Regretfully, as DSP was just a glint in someone's eye when I did formal education, many of the applied techniques I had to learn for myself in later life.Similarly coding theory was extremely basic back then, but it's key to what I do nowadays, again I am self-taught, but have benefitted from the many published practical works out there.What I wish I had paid more attention to was control theory. Doing PID loops for example is still a bit of a black art to me. I understand the concept, just not how to apply it, although I am sure I could pick it up if needs be.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: March 07, 2015, 02:04:13 am
content: Quote from: Howardlong on March 06, 2015, 09:18:05 amI couldn't work much of a differential equation if pressed on it, but I like to think I have enough of a framework to figure out where I need to go.A good example of applied diff eq: heat flow problems.Suppose you have a row of transistors attached to a heat spreader extending out from a heatsink. The spreader is not big enough to dissipate much power, in and of itself; its purpose is to carry the heat from the devices into the main heatsink body.If you model the transistors as a source of constant power density per length or area (not unreasonable, if they are closely packed, and you assume the heat flowing from "heatsink tab" into the spreader surface is evenly distributed over each tab), then you have the differential relation that, for each increment of distance from the heatsink, dx, the total power flow drops as -p dx.When you solve this (thankfully, it's solvable with a mere integral -- one of the more trivial cases, as differential equations go!), you find that the temperature (as a function of distance along the heat spreader, from the heatsink to the end) follows a parabola: rising sharply (from heatsink temperature) at the root, then slowing down, until at the very tip, temp rise ceases (dT/dx = 0) and temperature is at its maximum (i.e., the parabola is a "downward opening" shape, with the vertex at the loose end of the heat spreader). And the total temp rise is simply the difference between a point on the parabola, and the vertex.When you run the numbers, using typical material properties, you find that, for low power applications, like sucking the heat out of a modest analog circuit, CPU board, small power amplifier, stuff like that -- you can do a pretty reasonable job with a hunk of modest-thickness aluminum, bolted to a heatsink on one end. (Maybe you'd bolt the PCB to the plate with a Gap-Pad inbetween, and use SMT and via-in-pad heatsinking on the board. Nice low-profile stuff.) By using conduction instead of convection, you avoid resorting to a fan (unreliable, dusty!) or worse methods, and it can also operate in a vacuum (if you ever find yourself needing to design physics instruments or aerospace hardware..). And the low profile can be packed densely, if you need it.But for stuff like high power switching and amplifying, where you need to pull hundreds of watts out, even with water cooling on the main heatsink, you're looking at either a massive copper billet to carry that heat, or a huge temp rise. So it gets unreasonable. In those cases, you need a more aggressive method -- devices right on the heatsink (so it gets rather bulky, but you have no choice), or some other method, like water cooling (needs special heatsinks or $$$ machining!).So, you can run some pretty nice analyses to determine go / no-go strategies, like this heatsinking example. Still stuff you might pick up by reading a book or from experience, but oddball cases like this are often rare enough that it's worth doing, because... if you haven't seen it before, what are the chances you'll even be able to find a reference?Another example I've done: dissipation from an "infinite" flat sheet. Suppose you bolt a transistor to the middle of a sheet. The sheet exhibits convection dissipation, at a rate (power per area) proportional to temperature. It's also laterally conductive. This is a radial problem, because heat will diffuse radially; but the convection (even for such a pitifully simple model of convection!) means it won't simply be a radial diffusion problem.As an example, if the sheet is heatsinked at some known radius, does not exhibit heat loss from the surface, and the transistor has some effective radius (i.e., how big the heatsink tab is), then the temp rise is simply proportional to ln(R/r) -- a classic coaxial situation, invoking the log of the ratios. In this case, an infinite sheet would have infinite temp rise, but that's clearly unrealistic as it's not even representative to have an *infinite* sheet with no dissipation of its own; it's also noteworthy that a zero-diameter (point source) transistor will exhibit infinite temp rise, but that's quite logical because... well, if it's zero size, it's not very well connected, is it? That's like trying to dissipate heat down a thin wire, it ain't gonna happen.As it turns out, the specific-heat-loss case is just such an example without an analytical solution -- however, it's not all bad, because the function which does solve it, the Bessel function J0(x), is well studied. So you can still reach some semi-empirical but fully valuable conclusions, like: what is the radius of 90% temperature, 50%, 10%, etc; the lateral heat spreading rate (which is indeed a diffusive relation, taking sqrt(conductivity) or something like that), and so on.If you plug in typical numbers for a PCB, you find that the lateral heat spreading distance is around 20-40mm, i.e., leaving more than 20-40mm between power devices on the board will not substantially increase your ultimate power dissipation per device. Which is something you might intuit by experience or rules of thumb, but you'll have no idea how gross those conclusions are unless you evaluate the space from which they arise; and this way, you've found out something about the world, which is great.QuoteI picked up easily on Control Theory and DSP; they merely introduced State Space, which I wish there was more of in an undergrad curriculum.Even so, if you can reduce all your problems to a couple-pole approximation, you're not doing terrifically bad. If you can get a grasp on the nonlinearities of the system, and correct for them, you can still implement the same old solution. Seems to me, that was more the intention.Among those classes, I think the most egregious error (at least in the class I took) was teaching control theory exclusively abstract. I suspect I was the only kid in the class who had any idea what was going on, because I had solved those equations and systems myself, and knew where the R and C terms go.Or in your case, where the PID terms go.What's cool about stability criteria is, watching how poles interact (with respect to, inserting additional poles in the loop, varying gain, etc.). There are some very specific results, like: raising the gain on a two-pole system (I think?) causes the poles to migrate along the real axis, then merge (at first, the system is overdamped, and the poles are far apart: imagine an RCRC lowpass filter, which has the best case condition that the poles are nearly repeated, and that's it), then split again, along the imaginary axis. The system is guaranteed stable, at any gain, because the poles will not migrate into the right half plane (the real component remains constant). But, the magnitude of overshoot or ringing (the angle of atan(imag/real)) will get arbitrarily bad, until it might as well be oscillating. Add in non-idealities (like the inescapable time delay in physical systems, which can only be crudely approximated with poles, or gain or time constants which vary with operating point) and you'll probably find spontaneous (if bounded) oscillation at some point.Higher pole systems, as you ramp up the gain, often behave where one pole remains on the real axis (moving around some), but two get pushed together, then apart as a complex pair, and they drift towards the imaginary axis, and eventually cross into the RHP where true spontaneous oscillation is guaranteed. The angle of this approach is determined by... something about the system, I forget if it's the number of poles (therefore, for N = 3, you get 60 degree trajectories or whatever), or their proportions, or what.And in any of these cases, you want to pick the gain which gives the desired damping, plus freedom from component tolerances and all that.The exact DSP analogy is the Z Transform, and instead of "poles in RHP", you're looking at poles outside the unit circle. Everything works out much the same; there exists a transform between Z and s (Laplace) domain transfer functions. So any real (pole and zero) analog filter can be implemented (within limits of Nyquist and all, of course) exactly as a Z domain (delayed taps plus MAC, FIR or IIR) filter.Tim

author: codeboy2k
author_rank: Super Contributor
timestamp: March 07, 2015, 02:44:41 am
content: For control theory reviews, I really like this person's channel:https://www.youtube.com/channel/UCq0imsn84ShAe9PBOFnoIrg

author: Howardlong
author_rank: Super Contributor
timestamp: March 07, 2015, 03:01:37 am
content: Thanks Tim, I'll take an in depth look at your reply later.The differential equation I was referring to was relating to a real pendulum with excessive deviation and subject to fluid friction. It's been a long time, but essentially the static and dynamic friction mean you end up with a nonlinear diff eq which is not solvable analytically, it is in fact chaotic. However you want to try it you have to do it numerically in cold hard numbers. I did it in an enhanced embedded Z80 MPU in C in real time. I even wrote my own floating point library... which worked, but performed far worse than the super tuned version I ended up purchasing.Classical pendulum solutions don't work for excessive deviation, ie up to and including the pendulum going all the way around it axis, as the friction, partciularly the dynamic friction, becomes a far more fundamental and key part of the solution.Luckily I don't do that stuff any more, but I have been known to do my fair share of orbital mechanics in the interim ;-)

author: T3sl4co1l
author_rank: Super Contributor
timestamp: March 07, 2015, 03:18:40 am
content: Quote from: Howardlong on March 07, 2015, 03:01:37 amAh, so you've been quite deep in that kind of $&%!, lovely.Tim

author: CatalinaWOW
author_rank: Super Contributor
timestamp: March 07, 2015, 03:27:47 am
content: It can be a vicious loop. You remember what you use, and you don't use what you don't remember. Once you start running to the calculators (or the smart guy down the aisle) it can fade pretty fast. I've watched it happen to many of my peers. For me algebra, trig, simple calculus and differential equations along with basic probability theory have stuck with me. Same with much of linear algebra. But contour integrals, Lebesgue integrals and most of the theory of random functions is gone with the wind. Along with many other things I can't even remember the names of.Guys who do antenna design and radio propagation will retain a different set than the ones who are doing circuit design, or those designing diffusion processes.

author: turbo!
author_rank: Regular Contributor
timestamp: March 07, 2015, 04:39:28 am
content: Yes, I can still math. It's the principle that counts, not how to do it. I love the concepts.High school kids are probably way better than I am at long division or differentiation by handNow, I have very good understand of derivatives, integrals despite getting a C in calculus.

author: radiomog
author_rank: Regular Contributor
timestamp: March 07, 2015, 04:49:42 am
content: there are a few things I use a formulae for, but not much..It is 'run an app/ program or software' and plug in the numbers to get the results you want, anymore.

author: HP-ILnerd
author_rank: Frequent Contributor
timestamp: March 07, 2015, 05:01:11 am
content: Strangely, I'm better now than when I was in school. Probably because I developed an interest in the subject rather than was just required to know it.I've even got some phone Apps that teach how to do arithmetic tricks in your head. That sort of thing is never comprehensive, but it covers a lot of common territory, and more importantly, they work!

author: Rerouter
author_rank: Super Contributor
timestamp: March 07, 2015, 05:12:17 am
content: HP on that subject, It wasnt until 2 years after high school that i came across someone else teaching a kid how to transpose equations with fractions that it clicked, he was using a 2x2 grid and fridge magnet letters, the vertical line being the = sign, and the horizontal line being the fraction, to solve any of them, you can only move the elements in diagonals,that would have helped very very much in physics and engineering in high-school.... but i digress,

author: JohnnyBerg
author_rank: Frequent Contributor
timestamp: March 07, 2015, 09:13:16 am
content: What helps when doing math is a feeling off the numbers your'e supposed to get.Some examples:- I had to calculate a inductor and transformer for a SMPS with PFC . I'd got 350 windings for the PFC coil, and a flux through the core of 2.3T. Normal values? Nope, any insider will see that these must be wrong.- I'd put one my references in a oven, measured drift and calculated the drift over the whole temperature range. Thats very simple math. I've got 0.004ppm/C. Any insider will see that the bullshit meter went through the roof.Please calculate, and search you're feelings about the outcome:Thevenins law: a current source has a value of 5 Amps and a internal resistance of 5 Mega ohm. What is the voltage when no load is applied?

author: Refrigerator
author_rank: Super Contributor
timestamp: March 07, 2015, 09:30:37 am
content: It's funny how they teach you all this math at school but you end up not using any of it 99.9 % of the time.

author: Cside
author_rank: Regular Contributor
timestamp: March 07, 2015, 10:02:26 am
content: Quote from: EEVblog on March 06, 2015, 06:42:26 amAs if you ever could solve an integral.Not fooling anyone Dave.Edited - In case it isn't obvious this comment is not to be taken literaly, facetiously or in any way other than pure jest. Cside cannot be held accountable for feelings of offense or depression or otherwise badwill by misinterpretation, misunderstanding or misuse of the stated comment. All rights reserved batteries solved separately.

author: Red Squirrel
author_rank: Super Contributor
timestamp: March 07, 2015, 10:16:08 am
content: I can't math my way out of a paper bag, but I can probably write a program to accomplish the same thing. New at electronics and learning, but I see the math part might be of a challenge. I'm more of the type "let's slap on a bigger resistor here and see what happens" kind of guy.Probably not the best approach eh.

author: Galenbo
author_rank: Super Contributor
timestamp: March 07, 2015, 10:31:01 am
content: I've forgotten some things about differential equitation and matrix operations, but still know what's about.The few times I needed something I forgot, I never needed much time to refresh it.

author: lapm
author_rank: Frequent Contributor
timestamp: March 07, 2015, 12:09:41 pm
content: Personally i haven needed derivates/integrals at all since school 20 years ago... And they claimed its important in life for more then some fancy math...I get by just fine with basic maths, datasheets diagrams, etc... But then again i work at brewery, no high-tech or cutting edge research there when your just operator of production line... I have forgotten so much math and how to do it... But then again i have those school math boks still stored away, so if i need them, i can go look it up...

author: HighVoltage
author_rank: Super Contributor
timestamp: March 07, 2015, 02:17:53 pm
content: Math was always a hobby for me ... but ...the last three years I helped a family member to pass the German Abitur with advanced math and physics. And I was confronted with the fact, that I had to look up certain rules of integration and differentiation that I had forgotten for some reason. It surprised me. Well, she passed he Abitur with a really good grade and my math skills got refreshed. It was a win win.

author: nixfu
author_rank: Unknown
timestamp: March 07, 2015, 02:21:52 pm
content: This thread has inspired me to go find some calculus on-line courses to go through and refresh my skills.Honestly, I have been meaning to do that anyway, because every time I feel like watching videos from an online EE class that seems interesting and there are some that are interesting about topics I did not get in school or that are newer topics since then, the problem I have is that they are so math heavy in university that I just think to myself "bah, math, I forgot most of that" and give up on those classes.It would be nice to be able to actually easily follow what they are doing again.

author: Sparks
author_rank: Contributor
timestamp: March 07, 2015, 11:34:41 pm
content: So this would appear to be somewhat normal then. Back in high school I would do most of my algebra in my head, failed 3 times for not showing work.Even when working the problem in front of the teacher, right answer, still a zero for not showing work. Slowing down to write it out would always mess me up.What could I do? Now in college they give credit and dont care how you get the answer, too bad it's taking forever to remember how to do the work. Just a fight againt the clock to remember what I didn't even know I forgot.