## Search found 104 matches

- Wed May 11, 2016 5:27 pm UTC
- Forum: Mathematics
- Topic: Seemingly simple
- Replies:
**16** - Views:
**2726**

### Re: Seemingly simple

good job encouraging contributions to this forum

- Wed May 11, 2016 3:09 pm UTC
- Forum: Mathematics
- Topic: Seemingly simple
- Replies:
**16** - Views:
**2726**

### Re: Seemingly simple

who is "we"? - for that matter the Euclidian metric is "wrong" too for something constructed on the Earth's surface... I'm modeling a roof that's going to have diagonal purlins (cross supports) coming from two angles and is going to need some custom brackets; B is the spacing bet...

- Wed May 11, 2016 12:38 am UTC
- Forum: Mathematics
- Topic: Seemingly simple
- Replies:
**16** - Views:
**2726**

### Re: Seemingly simple

for engineering values of "exact", you can set numerical entry/display number of digits up to 15 digits besides just dragging segment endpoints and watching the dynamically updated display of length on the right; you can enter numerical pair defined points or vectors or segments can be cre...

- Tue May 10, 2016 5:53 pm UTC
- Forum: Mathematics
- Topic: Seemingly simple
- Replies:
**16** - Views:
**2726**

### Re: Seemingly simple

don't need to create equations, solve by hand when you can just draw in GeoGebra http://www.geogebra.org/

all done with the construction tools

all done with the construction tools

- Fri Mar 25, 2016 2:50 pm UTC
- Forum: School
- Topic: Forum Migration
- Replies:
**403** - Views:
**487600**

### Re: Forum Migration

how do I get to the current comic page from the forum? - "xkcd" in the banner doesn't appear to be a link (IE11)

- Wed Mar 02, 2016 11:35 pm UTC
- Forum: Mathematics
- Topic: Math: Fleeting Thoughts
- Replies:
**378** - Views:
**99443**

### Re: Math: Fleeting Thoughts

Also, geometric algebra is gross. I wouldn't try to sell it to mathematicians but Hestenes reboot of Clifford's, Grassman's ideas for physics, engineering math extends how far can be gotten in one system before Tensors are needed Gibbs/Heaviside Vector Algebra is pretty lame in that context, even i...

- Wed Mar 02, 2016 8:32 pm UTC
- Forum: Mathematics
- Topic: Math: Fleeting Thoughts
- Replies:
**378** - Views:
**99443**

### Re: Math: Fleeting Thoughts

abs, norm seem inhibiting, squaring isn't going to be always safe when I want to derive/"prove" an equality in Geometric Algebra - which like Complex Valued equations needs conjugates for norms and has nilpotents I'm still struggling with the algebraic manipulations as it is - I suppose &q...

- Wed Mar 02, 2016 4:50 pm UTC
- Forum: Mathematics
- Topic: Math: Fleeting Thoughts
- Replies:
**378** - Views:
**99443**

### Re: Math: Fleeting Thoughts

is/are there good symbols, ways to write "equal up to a sign" in an equation?

- Tue Dec 01, 2015 6:24 pm UTC
- Forum: Science
- Topic: Acoustical Question of Squeaky Claps
- Replies:
**9** - Views:
**4752**

### Re: Acoustical Question of Squeaky Claps

diffraction can be interesting - I used to work next to a large warehouse with a vertical running corrugated iron siding - 100+ long

you could hear a chirp frequency in the backscatter echo when clapping, slamming our building's back door

I would look at Bragg diffraction for explaining that

you could hear a chirp frequency in the backscatter echo when clapping, slamming our building's back door

I would look at Bragg diffraction for explaining that

- Tue Dec 01, 2015 6:13 pm UTC
- Forum: Mathematics
- Topic: Greatest Mathematician of all time?
- Replies:
**65** - Views:
**15409**

### Re: Greatest Mathematician of all time?

Q: When did Bourbaki stop writing books?

A: When they realized that Serge Lang was a single person...

A: When they realized that Serge Lang was a single person...

- Sat Nov 14, 2015 11:18 pm UTC
- Forum: Mathematics
- Topic: Linear approximation of a sphere
- Replies:
**7** - Views:
**1603**

### Re: Linear approximation of a sphere

not exact match but http://arxiv.org/pdf/1301.0496.pdf treats the spherical case late in the paper - has some refs that look worth a look too just my hobby horse - not that I'm able to do calculus in it yet: Quaternions or often better "Geometric Algebra" could be helpful for playing on sp...

- Thu Oct 15, 2015 5:08 am UTC
- Forum: Science
- Topic: Skin Effect in Electrolytes?
- Replies:
**2** - Views:
**1634**

### Re: Skin Effect in Electrolytes?

skin effect usually only matters at high AC frequencies - not many try to send high frequency AC through electrolyte solutions - electrochemistry is very largely done at DC sometime some AC is superimposed to modify electrode/electrolyte boundary layer structure/ion transport kinetics the magnitude ...

- Fri Sep 18, 2015 3:57 am UTC
- Forum: Science
- Topic: Is velocity a limit?
- Replies:
**18** - Views:
**3590**

### Re: Is velocity a limit?

there's velocity: the vector, acceleration too - vectors often written in bold: v, a

- Tue Sep 08, 2015 1:27 am UTC
- Forum: Science
- Topic: Human Body Parts MTTF
- Replies:
**3** - Views:
**1561**

### Re: Human Body Parts MTTF

its not just the budgeting - some have moral issues with buying low mileage replacements off of disadvantaged youth - though at my age it seems like a better and better idea as long as you keep it regulated, don't go black market https://en.wikipedia.org/wiki/Organlegging of course that was in the c...

- Thu Sep 03, 2015 9:01 pm UTC
- Forum: Science
- Topic: Different sized wheels, one axle, rolling down an incline
- Replies:
**15** - Views:
**3107**

### Re: Different sized wheels, one axle, rolling down an inclin

you're assuming the wheels are rigidly attached to the axle ? in either case you are missing term(s) in the angular moment of inertia - its a Tensor ( but its a "simple" 3x3 matrix ) each disk has a orthogonal pair of principle moments perpendicular to the axle in addition to the moment ab...

- Tue Sep 01, 2015 2:33 pm UTC
- Forum: Science
- Topic: Different sized wheels, one axle, rolling down an incline
- Replies:
**15** - Views:
**3107**

### Re: Different sized wheels, one axle, rolling down an inclin

since the question is only asking for the initial accelerations with the motion constraint fixed by the given geometry, the moment of inertia tensor is needed for a accurate answer since the discs both rotate about the axle and are also turning about the coning point which does put it beyond most un...

- Sun Jul 05, 2015 4:38 pm UTC
- Forum: Science
- Topic: Question regarding angular momentum.
- Replies:
**4** - Views:
**1385**

### Re: Question regarding angular momentum.

you can hold the assembly while spinning up and then it should stay still after you let go if the speed of the flywheels, angular momentum of the whole doesn't change (+/- Earth's rotation) if you change the net angular momentum with flywheel speed changes when its free then the whole assembly shoul...

- Sun Jun 28, 2015 7:24 pm UTC
- Forum: Coding
- Topic: Does anyone use Processing?
- Replies:
**2** - Views:
**2450**

### Re: Does anyone use Processing?

left handed coordinates, again? - what's wrong with programmers?

- Fri Jun 26, 2015 8:48 pm UTC
- Forum: Mathematics
- Topic: Greatest Mathematician of all time?
- Replies:
**65** - Views:
**15409**

### Re: Greatest Mathematician of all time?

There is one mathematician I haven't seen mentioned here, and while I certainly wouldn't call him the "greatest of all time", I personally find quaternions fascinating, especially their (asserted) connection/relation to space-time. Hamilton, I would love to discuss relativity with you and...

- Sat Jun 13, 2015 1:08 pm UTC
- Forum: Coding
- Topic: Reflection around the inside of a circle
- Replies:
**4** - Views:
**2740**

### Re: Reflection around the inside of a circle

you could use a Vector Math package for Java 2D isn't too hard to do just by component if you want to see all the nitty gritty our common version of vector math dates from the 1880's - although Grassman really did all you need by 1840 vector algebra seems to have taken a long time from Cartesian coo...

- Mon Apr 13, 2015 10:00 pm UTC
- Forum: Mathematics
- Topic: Why can't sine waves carry huge amounts of data?
- Replies:
**5** - Views:
**1580**

### Re: Why can't sine waves carry huge amounts of data?

to encode information you have to change something about your carrier signal - that requires a bandwidth, can't be done with "a xx Hz sine" changing the sine is Modulation - the resulting signal has more than just the original single sine frequency in its Fourier representation in the real...

- Mon Feb 02, 2015 5:27 pm UTC
- Forum: Mathematics
- Topic: Drum Math
- Replies:
**1** - Views:
**1017**

### Re: Drum Math

more an engineering inquiry - likely not much to interest to modern math types with the actual math used well over a century old even though its elaboration in shell theory and nonlinear dynamics like buckling still keep engineering "theory" types busy with applied math that takes a good d...

- Wed Jan 07, 2015 6:58 pm UTC
- Forum: Mathematics
- Topic: Which order to learn math topics in?
- Replies:
**24** - Views:
**12899**

### Re: Which order to learn math topics in?

Which order to learn math topics in? what do you want to do with "math"? - ultimately math can be viewed as abstract "games with symbols" - and way "meta" about what types games are possible but as an engineer I can assure you that lots of highly technical professions ...

- Fri Oct 17, 2014 4:31 pm UTC
- Forum: Science
- Topic: Flying cars and jet-powered batwing
- Replies:
**110** - Views:
**23391**

### Re: Flying car (engineering heavy)

https://www.google.com/#q=cartercopter does VTOL, but can't hover

- Tue Sep 23, 2014 4:55 pm UTC
- Forum: Mathematics
- Topic: The Three Squares Problem
- Replies:
**10** - Views:
**3736**

### Re: The Three Squares Problem

oops, forgot the alternating signs from the i^(n)

I need to remember CAS is only a clik away

integral test gives the divergence of the 1/(n^2+1)^(1/2) sum

I need to remember CAS is only a clik away

integral test gives the divergence of the 1/(n^2+1)^(1/2) sum

- Tue Sep 23, 2014 1:43 pm UTC
- Forum: Mathematics
- Topic: The Three Squares Problem
- Replies:
**10** - Views:
**3736**

### Re: The Three Squares Problem

I think using Pythagoras defining sin(theta)=1/(n^2+1)^(1/2) is simpler than using tangent, and with sin(theta) you can use the small angle approximation directly some convergence tests: https://www.math.hmc.edu/calculus/tutorials/convergence/ Edit, err- wrong: for divergence argument it helps that ...

- Mon Sep 22, 2014 2:14 pm UTC
- Forum: Mathematics
- Topic: Math: Fleeting Thoughts
- Replies:
**378** - Views:
**99443**

### Re: Math: Fleeting Thoughts

the Geometric Algebra site I pointed to is meant as an elementary introduction - there is more depth, history easily found by just quoting Geometric Algebra in search in that order Some seem to object to "Geometric Algebra" being used as a name - but Grassman who invented the exterior prod...

- Wed Sep 17, 2014 10:48 pm UTC
- Forum: Mathematics
- Topic: Math: Fleeting Thoughts
- Replies:
**378** - Views:
**99443**

### Re: Math: Fleeting Thoughts

the Geometric Algebra approach to trig proofs may be new to some http://geocalc.clas.asu.edu/GA_Primer/G ... eting.html

http://geocalc.clas.asu.edu/GA_Primer/G ... index.html (has answer page)

http://geocalc.clas.asu.edu/GA_Primer/G ... index.html (has answer page)

- Fri Jul 25, 2014 3:54 pm UTC
- Forum: Mathematics
- Topic: Plotting complex functions
- Replies:
**2** - Views:
**1372**

### Re: Plotting complex functions

for MatLab like numeric sw I like http://www.scilab.org/ - not as MatLab compatible as the Octave - but appears to have much more support, active development, nice GUI... ( low level syntax is Matlab compatible, has a m-file translator) symbolic CAS is what I really want - but the free world is not ...

- Tue Jul 22, 2014 5:41 pm UTC
- Forum: Mathematics
- Topic: Quaternions
- Replies:
**28** - Views:
**4413**

### Re: Quaternions

I*j*k=-1 is weird - a choice of "handedness" that Gibbs swapped when he stole the name "vector" from Hamilton and gave them the present interpretation some GA authors do appear to adopt a 3D Bivector basis with Hamilton's i,j,k handedness convention but the uniform application of...

- Mon Jul 21, 2014 9:02 am UTC
- Forum: Mathematics
- Topic: Quaternions
- Replies:
**28** - Views:
**4413**

### Re: Quaternions

the Real valued Clifford Algebra that constitutes Hestenes "Geometric Algebra" seems to me a shorter path to understanding Quaternions - no imaginaries required - Bivectors do the right thing still have the sandwich multiplication rule for Rotors, and the required "conjugation" (...

- Sat Jul 19, 2014 4:43 pm UTC
- Forum: Mathematics
- Topic: Quaternions
- Replies:
**28** - Views:
**4413**

### Re: Quaternions

Geometric Algebra's smooth extension to higher dimensions enables easy extension to both the Homogeneous Projective model and the "Conformal" model http://en.wikipedia.org/wiki/Conformal_geometric_algebra This report aims to show that using the mathematical framework of conformal geometric...

- Fri Jul 18, 2014 12:59 pm UTC
- Forum: Mathematics
- Topic: Quaternions
- Replies:
**28** - Views:
**4413**

### Re: Quaternions

Hestenes reboot of Grassman's and Clifford's ideas as "Geometric Algebra" is a nice generalization, shows how complex numbers and Quaternions are analogous to Rotors in 2D and 3D GA respectively, and Rotors generalize to higher dimension the history is interesting itself - seeing how Gibbs...

- Wed May 14, 2014 11:04 pm UTC
- Forum: Science
- Topic: Ultimate Egg Drop Contest
- Replies:
**6** - Views:
**2067**

### Re: Ultimate Egg Drop Contest

from orbit?

- Sat May 03, 2014 9:18 pm UTC
- Forum: Mathematics
- Topic: Distance to the moon
- Replies:
**5** - Views:
**2333**

### Re: Distance to the moon

another fun search: https://www.google.com/#q=ham+low+power+eme

apparently radio amateurs have been bouncing radio off the moon for a while, now for a US k$ or two in equipment

apparently radio amateurs have been bouncing radio off the moon for a while, now for a US k$ or two in equipment

- Fri May 02, 2014 11:00 pm UTC
- Forum: Mathematics
- Topic: Distance to the moon
- Replies:
**5** - Views:
**2333**

### Re: Distance to the moon

lunar star occultation timing across hundreds or even a thousand mile baselines would be easy today with internet collaboration, GPS time/coordinate info http://www.lunar-occultations.com/iota/bstar/bstar.htm http://www.icq.eps.harvard.edu/MagScale.html or just apparent motion/parallax against the b...

- Sat Mar 08, 2014 4:33 pm UTC
- Forum: Mathematics
- Topic: Imaginary Numbers and Trig Question
- Replies:
**5** - Views:
**2176**

### Re: Imaginary Numbers and Trig Question

complex numbers can be considered to encode rotation and scaling, search for complex or imaginary numbers and rotation will lead to lots of material http://betterexplained.com/articles/a-visual-intuitive-guide-to-imaginary-numbers/ may be a really simple start the next step from 2D plane rotation is...

- Fri Mar 07, 2014 5:34 am UTC
- Forum: Hardware
- Topic: Laptop/phone's headphone jack as a DAC
- Replies:
**8** - Views:
**5463**

### Re: Laptop/phone's headphone jack as a DAC

audio outputs are usually AC coupled - can't put out a constant DC value often both a DC blocking series Capacitor is used and the audio DAC itself has a digital high pass filter built in if you only want audio frequency AC you're fine except for level calibration but for converting audio AC to a DC...

- Fri Jan 24, 2014 4:32 am UTC
- Forum: Mathematics
- Topic: Matlab alternatives
- Replies:
**4** - Views:
**1835**

### Re: Matlab alternatives

SciLab has very active development and there are m file translators although Octave is supposed to be more nearly MatLab m file compatible there is a place for these defined environments for those who don't want to write a real program for each and every thing they need to do - and they still have i...

- Wed Jan 22, 2014 11:58 pm UTC
- Forum: Mathematics
- Topic: Math Software
- Replies:
**143** - Views:
**136216**

### Re: Math Software

it appears that Cinderella dynamic plane geometry software went free for the full version this past fall http://www.cinderella.de/tiki-index.php haven't done anything with it yet but skimmed the Doc - I have more hours with the similar (but possibly more ad hoc) Geogebra which is also free http://ww...