### Author Topic: Finding local max, min, and saddle point  (Read 1755 times)

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#### trmpereira

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##### Finding local max, min, and saddle point
« on: June 07, 2013, 01:47:56 pm »

Define sela()=
Prgm
:Local f,fx,fy,mat,fxx,fyy,a,fxxpo

©fx-> first derivative in terms of X
©fy-> first derivative in terms of Y
©mat->Trying to make extraction of coordinate point (x,y) to use in second derivative in terms of X with P0(x,y), doesnt work! Accept suggestion

©fxx and fyy second derivative in terms of respective var

©a to store coordinate point I really need HELP here! How can I use or put this two points in two different variables?

:Request "Function",f
:fx:=d/dx(f,x)
:fy:=d/dy(f,y)
:fxx:=d/dx(fx,x)
:fyy:=d/dy(fy,y)

:a:=solve(system(fx=0,fy=0),{x,y})

:fxxpo:=solve(fxx=0,x)|a

©Ok! i believe inst a good solution here if a get a "a" like this: x=−1 and y=−1 or x=0 and y=0 or x=1 and y=1 What im gonna do?

:mat:=newMat(1,2)
:mat[1,1]:=fx ©Make a new line for description
:mat[1,2]:=fy
Disp fx
Disp fy
Disp mat
Disp fxx
Disp fyy
Disp a
Disp fxxpo
Disp x
Disp y
:
:EndPrgm

#### Keoni29

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##### Re: Finding local max, min, and saddle point
« Reply #1 on: June 07, 2013, 03:32:00 pm »
Your text formatting is weird. What is up with that? Also use [ code][/ code] tags.
« Last Edit: June 07, 2013, 03:32:11 pm by Keoni29 »
If you like my work: why not give me an internet?

#### Streetwalrus

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##### Re: Finding local max, min, and saddle point
« Reply #2 on: June 07, 2013, 05:37:50 pm »
You should give more details. What kind of function are you studying ?

#### trmpereira

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##### Re: Finding local max, min, and saddle point
« Reply #3 on: June 19, 2013, 10:30:25 pm »
Sorry for delay but I find the solution instead of solve() I use zeros... and voialá!
« Last Edit: June 19, 2013, 10:30:59 pm by trmpereira »

#### imath

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##### Re: Finding local max, min, and saddle point
« Reply #4 on: June 30, 2013, 12:42:20 am »
a:=solve(system(fx=0,fy=0),{x,y})
I remeber it's wrong.
we should use zeros() because it returns a list.