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This forum is locked: you cannot post, reply to, or edit topics. TI-Basic Brain Teasers => TI-BASIC
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thornahawk
μολών λαβέ


Active Member


Joined: 27 Mar 2005
Posts: 569

Posted: 10 Apr 2008 12:16:28 am    Post subject:

Without using any of the LinReg commands, write the smallest possible linear regression routine that, given the x-coordinates stored in L1 and the y-coordinates stored in L2, will output the slope and y-intercept of the best-fit line of a given set of points.

You can of course check the validity of your routine by comparing results with any of the two LinReg functions. ;)

thornahawk
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emperorwiggy


Newbie


Joined: 27 Mar 2008
Posts: 27

Posted: 10 Apr 2008 07:12:36 am    Post subject:

Is there any particular reason why you can't use the LinReg command? Besides making it really hard? :biggrin:
I could do it with a numstring subroutine that doesn't use linreg, but I don't have one.
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DarkerLine
ceci n'est pas une |


Super Elite (Last Title)


Joined: 04 Nov 2003
Posts: 8328

Posted: 10 Apr 2008 08:29:23 am    Post subject:

This is probably cheating:
Quote:
e^(L2→L2
ExpReg
ln({b,a


I suggest the rules be changed to not allow use of any regressions (including LinRegTTest, or on the newer calculators LinRegTInt)


Last edited by Guest on 10 Apr 2008 08:32:39 am; edited 1 time in total
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thornahawk
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Joined: 27 Mar 2005
Posts: 569

Posted: 10 Apr 2008 09:52:27 am    Post subject:

"Besides making it really hard?"

- Well, the name of the forum has "Brain Teasers" in it, so... ;)

"This is probably cheating..."

- Yes it is. :P

"I suggest the rules be changed to not allow use of any regressions (including LinRegTTest, or on the newer calculators LinRegTInt)"

- Yes indeed. No built-in regression functions please, Louise. :P

thornahawk
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DarkerLine
ceci n'est pas une |


Super Elite (Last Title)


Joined: 04 Nov 2003
Posts: 8328

Posted: 10 Apr 2008 09:44:06 pm    Post subject:

Okay, here's an honest attempt:

Quote:
2-Var Stats
Matr►list(rref([[Σx²,Σx,Σxy][Σx,n,Σy]]),3,L₃


The routine outputs the result in L₃ as the pair {slope, y-intercept}. If you want the result to be displayed as well, add L₃ as a final line.


Last edited by Guest on 02 Aug 2010 02:33:09 am; edited 1 time in total
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thornahawk
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Active Member


Joined: 27 Mar 2005
Posts: 569

Posted: 11 Apr 2008 12:39:00 am    Post subject:

Wow, that is short! Very Happy Here was my attempt:

Quote:
mean(L₁→T
mean((L₁-Ans)L₂)/mean((L₁-Ans)
{Ans,mean(L₂)-AnsT


thornahawk
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Weregoose
Authentic INTJ


Super Elite (Last Title)


Joined: 25 Nov 2004
Posts: 3976

Posted: 11 Apr 2008 08:48:44 am    Post subject:

Where X = and Y = :
Quote:
2-Var Stats
(Σxy-nXY)/(Σx-nX
{Ans,Y-XAns

[EDIT]

That's basically what thornahawk had. Surprised
My sources were (27) and (2Cool from here.


Last edited by Guest on 11 Apr 2008 09:04:22 am; edited 1 time in total
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DarkerLine
ceci n'est pas une |


Super Elite (Last Title)


Joined: 04 Nov 2003
Posts: 8328

Posted: 11 Apr 2008 01:33:30 pm    Post subject:

A minor optimization to the second line of your routine: (Σxy/n-XY)/σx²

Last edited by Guest on 02 Aug 2010 02:32:56 am; edited 1 time in total
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