# Suggest a function

1. Sep 28, 2008

### TalonStriker

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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2. Sep 28, 2008

### arildno

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

3. Sep 28, 2008

### TalonStriker

you missed the part where I said that I didn't want trig functions.

4. Sep 28, 2008

### Hootenanny

Staff Emeritus
tanh isn't a trigonometric function.

5. Sep 28, 2008

### sutupidmath

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

Last edited: Sep 28, 2008
6. Sep 28, 2008

Look at the class of logistic functions.

7. Sep 28, 2008

### sutupidmath

Mine doesn't really work, since i didn't see the restriction that it has to have a horizontal asymptote.

8. Sep 29, 2008

### Integral

Staff Emeritus
The http://en.wikipedia.org/wiki/Error_function" [Broken] come close to what you want.

Last edited by a moderator: May 3, 2017
9. Sep 29, 2008

### arildno

What nonsense.
Do you think you can't "apply" an arctan function just because you are not dealing with a problem in trigonometry???

10. Sep 29, 2008

### Count Iblis

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. Sep 29, 2008

### St. Aegis

just use integral's curves lawl