** UnhandledExceptionEventHandler :: OFFICIAL LC / CHATTER THREAD ** - Page 516 - Computer Technical Help

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03-19-2014 , 05:11 PM

#12876

Ryanb9

Carpal \'Tunnel

Join Date: Aug 2006 Posts: 7,566

Assuming " d/dx " and " ' " mean the same thing (derivative of) am I the only one who sees infinite recursion here?

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03-19-2014 , 05:51 PM

#12877

candybar

Pooh-Bah

Join Date: Aug 2011 Posts: 4,375

Quote:

Originally Posted by Ryanb9

Assuming " d/dx " and " ' " mean the same thing (derivative of) am I the only one who sees infinite recursion here?

(f(kx + b))' and f'(kx + b) are not the same thing.

let f(x) = x^2
f'(x) = 2x

Using the rule:

(f(kx + b))'
= kf'(kx + b)
= k(2kx + 2b)
= 2*(k^2)*x + 2kb

Or the standard way:

(f(kx + b))'

= ((k^2)*(x^2) + 2kbx + b^2)'
= 2*(k^2)*x + 2kb

Quote

03-19-2014 , 05:55 PM

#12878

gaming_mouse

Carpal \'Tunnel

Join Date: Oct 2004 Posts: 13,786

there's no recursion because f' in this case can be taken to mean "the formula for the derivative of f(x), but evaluated at (kx + b)".

So you start off knowing what f(x) and f'(x) are, and now you want to know what (f(kx+b))' is. The answer is put kx + b into your formula f', and then multiply the whole result by k.

This is just a special case of the chain rule, btw.

Last edited by gaming_mouse; 03-19-2014 at 05:59 PM. Reason: clarify notation

Quote

03-19-2014 , 05:56 PM

#12879

candybar

Pooh-Bah

Join Date: Aug 2011 Posts: 4,375

Btw I think this is the more general rule:

d/dx f(g(x)) = g'(x)f'(g(x))

Quote

03-19-2014 , 06:04 PM

#12880

gaming_mouse

Carpal \'Tunnel

Join Date: Oct 2004 Posts: 13,786

Quote:

Originally Posted by candybar

Btw I think this is the more general rule:

d/dx f(g(x)) = g'(x)f'(g(x))

yes, although I've always preferred the more suggestive (since it hints why it is true using infintesimals) formula:

Quote

03-19-2014 , 06:16 PM

#12881

Ryanb9

Carpal \'Tunnel

Join Date: Aug 2006 Posts: 7,566

Quote:

Originally Posted by gaming_mouse

Right, I mean if we give them the benefit of the doubt and play along, there is no recursion. I'm talking about if we look at it nittaly or just at face value.

Quote

03-19-2014 , 06:24 PM

#12882

e i pi

veteran

Join Date: Feb 2010 Posts: 2,230

stop using whatever book/notes is mixing notation in definitions. use this instead,

http://tutorial.math.lamar.edu/Class...fFormulas.aspx

Quote

03-19-2014 , 06:42 PM

#12883

clowntable

Carpal \'Tunnel

Join Date: Jun 2006 Posts: 45,557

We used f and f' and f'' etc. exclusively in high school and university it was all d/dx from the getgo...was a bit confusing at first but then again I think our high school math was more advanced than the first couple of university math classes.

[and 12th grade honors math (the stuff that gives >4.0) in the US was like 7th grade math but I blame that on...Oklahoma]

Quote

03-19-2014 , 09:48 PM

#12884

maxtower

Carpal \'Tunnel

Join Date: Sep 2005 Posts: 7,996

Quote:

Originally Posted by clowntable

I doubt Oklahoma is a unique situation in this.

Quote

03-19-2014 , 11:47 PM

#12885

suzzer99

Save the Cheerleader, Save the World

Join Date: Nov 2005 Posts: 101,163

This thread is triggering PTSD from differential equations class.

Quote

03-19-2014 , 11:53 PM

#12886

daveT

S.A.G.E. Master

Join Date: Jun 2005 Posts: 23,955

Quote:

Originally Posted by Ryanb9

Right, I mean if we give them the benefit of the doubt and play along, there is no recursion. I'm talking about if we look at it nittaly or just at face value.

I don't see anything wrong with the way it is written.

Quote

03-20-2014 , 09:25 AM

#12887

derada4

old hand

Join Date: Feb 2011 Posts: 1,544

So after being a dedicated Firefox user for about 8 years, I think I've just been converted to Chrome.

I'm surprised. I'm quite reluctant to change and within <2 min of using it I was like "wow, this is an objectively better browser".

It just feels a lot better: faster and more responsive. I don't know much about browsers, what is it exactly that's responsible for this?

Quote

03-20-2014 , 09:57 AM

#12888

clowntable

Carpal \'Tunnel

Join Date: Jun 2006 Posts: 45,557

From the HN comments of the crypto 101 post (wheee free crypto ebook)...pretty good intor video (not specific to Python):
https://www.youtube.com/watch?v=3rmCGsCYJF8

Quote

03-20-2014 , 10:34 AM

#12889

Nchabazam

Pooh-Bah

Join Date: Mar 2008 Posts: 4,938

Quote:

Originally Posted by derada4

What OS? I use chrome, but firefox feels significantly faster to me than chrome. I just don't like its layout.

edit: on Mac

Quote

03-20-2014 , 10:36 AM

#12890

suzzer99

Save the Cheerleader, Save the World

Join Date: Nov 2005 Posts: 101,163

Quote:

Originally Posted by derada4

Lack of programmable control keys tilts me about Chrome to no end. Ctrl-tab should toggle back and forth between two tabs (with an extension is fine, but you can't even build one to do that). And Ctrl–B should bold when I'm in this text box. That's literally my only beef with Chrome, but it's a big one.

Quote

03-20-2014 , 10:36 AM

#12891

suzzer99

Save the Cheerleader, Save the World

Join Date: Nov 2005 Posts: 101,163

Quote:

Originally Posted by Nchabazam

What OS? I use chrome, but firefox feels significantly faster to me than chrome. I just don't like its layout.

edit: on Mac

Firefox on Mac is pretty buggy. We don't even have to support it on our website.

Quote

03-20-2014 , 10:47 AM

#12892

Nchabazam

Pooh-Bah

Join Date: Mar 2008 Posts: 4,938

Quote:

Originally Posted by suzzer99

Firefox on Mac is pretty buggy. We don't even have to support it on our website.

It is a little buggy. It would flat out crash on like half the websites I visited until I upgraded to a new beta.

Quote

03-20-2014 , 11:31 AM

#12893

jjshabado

Carpal Tunnel

Join Date: Jul 2006 Posts: 22,732

What's the business case for something like Safari? Like why does Apple care at this point about having their own browser?

Quote

03-20-2014 , 12:27 PM

#12894

candybar

Pooh-Bah

Join Date: Aug 2011 Posts: 4,375

Quote:

Originally Posted by jjshabado

What's the business case for something like Safari? Like why does Apple care at this point about having their own browser?

If Chrome becomes the default browser on iPad/iPhone, it can become a dominant mobile platform in a hurry. Google's ability to add proprietary extensions to Chrome to make it a more attractive mobile platform is only limited by other popular browsers' refusal to do the same.

On desktop, IE and Firefox are credible alternatives but on mobile, it's going to be Chrome and Safari.

Quote

03-20-2014 , 01:20 PM

#12895

jjshabado

Carpal Tunnel

Join Date: Jul 2006 Posts: 22,732

Fair points, although I was thinking more of on desktops.

I guess maybe some of those same arguments apply there as well. If you have one dominant browser that isn't you you're at a disadvantaged for offering web based products.

Quote

03-20-2014 , 02:46 PM

#12896

maxtower

Carpal \'Tunnel

Join Date: Sep 2005 Posts: 7,996

I like having different browsers so I can log in to two different accounts on the same website and have my password remembered.

Maybe there is a smarter way to do this with one browser?

Quote

03-20-2014 , 03:59 PM

#12897

candybar

Pooh-Bah

Join Date: Aug 2011 Posts: 4,375

Quote:

Originally Posted by maxtower

I like having different browsers so I can log in to two different accounts on the same website and have my password remembered.

Maybe there is a smarter way to do this with one browser?

I have never used this feature until you just made me look but it looks like Chrome allows multiple users. And I thought Firefox had multiple profiles from a while back?