Find Function Like in Picture - No Trig Needed

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Discussion Overview

The discussion revolves around finding a mathematical function that resembles specific shapes shown in an attached picture, with the requirement that the function approaches constant limits as x approaches both positive and negative infinity. Participants express a preference for non-trigonometric functions, citing previous exposure to similar functions in differential equations.

Discussion Character

  • Exploratory
  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • One participant requests a function that resembles a specific shape without using trigonometric functions like arctan.
  • Another participant suggests the hyperbolic tangent function, noting it can be adjusted with constants and scaling.
  • A different participant reiterates the request for non-trigonometric functions, emphasizing that hyperbolic tangent is not a trigonometric function.
  • One participant proposes a piecewise function defined as f(x) = -x^(1/3) for x ≥ 0 and f(x) = (-x)^(1/3) for x < 0, while acknowledging it may not meet the requirement of having a horizontal asymptote.
  • Another participant mentions logistic functions as a potential class of functions to consider.
  • A suggestion is made to explore the error function as a possible candidate.
  • There is a discussion about the applicability of arctan despite the initial request to avoid trigonometric functions, leading to some contention among participants.
  • A participant inquires about the availability of numerical values or just the shape of the graph to help identify the function more accurately.
  • One participant humorously suggests using integral curves as a solution.

Areas of Agreement / Disagreement

Participants express disagreement regarding the use of trigonometric functions, particularly arctan, with some insisting on non-trigonometric options. The discussion remains unresolved as multiple competing views and suggestions are presented without consensus.

Contextual Notes

Some participants note the importance of having a horizontal asymptote, which may limit the applicability of certain proposed functions. There are also references to specific mathematical properties that may not be fully explored in the discussion.

TalonStriker
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Can anyone give me a function that (roughly) looks like the top or bottom one in the picture attached? And yes the limits is constant as x-> +/- infinity. I don't want a trig function like arctan since trig isn't really all that applicable for what I'm doing.

I'm posting here since I definitely saw functions like this in my deff eq class, but have unfortunately forgotten its formula.

Thanks.
 

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Well, the hyperbolic tangent function can achieve such behaviour easily, with addition of a constant, sign choice and scaling.
Similarly with the arctan function
 
arildno said:
Well, the hyperbolic tangent function can achieve such behaviour easily, with addition of a constant, sign choice and scaling.
Similarly with the arctan function

you missed the part where I said that I didn't want trig functions.
 
TalonStriker said:
you missed the part where I said that I didn't want trig functions.
tanh isn't a trigonometric function.
 
what about

[tex]f(x)=- x^{\frac{1}{3}},if,x\geq 0;(-x)^{\frac{1}{3}}, if, x<0[/tex] this is a piecewise defined funct.
 
Last edited:
Look at the class of logistic functions.
 
sutupidmath said:
what about

[tex]f(x)=- x^{\frac{1}{3}},if,x\geq 0;(-x)^{\frac{1}{3}}, if, x<0[/tex] this is a piecewise defined funct.

Mine doesn't really work, since i didn't see the restriction that it has to have a horizontal asymptote.
 
The http://en.wikipedia.org/wiki/Error_function" come close to what you want.
 
Last edited by a moderator:
TalonStriker said:
I don't want a trig function like arctan since trig isn't really all that applicable for what I'm doing.

you missed the part where I said that I didn't want trig functions.
What nonsense.
Do you think you can't "apply" an arctan function just because you are not dealing with a problem in trigonometry?
 
  • #10
And yes the limits is constant as x-> +/- infinity

Have you got accurate numerical values or just the shape of the graph? If you got numerical data you could take a shot at exactly guessing the function.
 
  • #11
just use integral's curves lawl
 

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