Find Inverse of Function w/ Floor: Tips & Tricks

  • Thread starter lewis198
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In summary, the conversation discusses finding the inverse of a function that contains a floor function. It is mentioned that the floor function itself does not have an inverse, but the function can be invertible on certain intervals. The solution involves defining x as a function of y and considering the periodicity of the function. It is also noted that the 'inverse' does not qualify as a function in technical terms. The conversation ends with the acknowledgement of the help received.
  • #1
lewis198
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I was wondering how you would find the inverse of a function if it contained a floor function.
Since I can't expand it, I can't set y as a function of x, so to speak. Should I use a series approximation?
 
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  • #2
* x as a function of y
 
  • #3
You keep talking about "containing" the floor function without explaining what you mean by that. In general a function has an inverse if and only if it is "one-to-one" and "onto". Since the floor function is not one-to-one- its value at any number between 0 and 1 is 1- 1 the floor function itself does not have an inverse. I cannot answer your question about functions "containing the floor function" because I do not know exactly what you man by one function "containing" another. Does f(x)= [1- floor(x)]+ floor(x) "contain the floor function? Is so then that is an example that does have an inverse: it is simply f(x)= x.
 
  • #4
This is what the equation looks like:

f(x)=A.[(x/T+rho)-floor(x/T+rho)]

I need to make x the subject of the equation, A,T and rho are constants.
 
  • #5
lewis198 said:
This is what the equation looks like:

f(x)=A.[(x/T+rho)-floor(x/T+rho)]

I need to make x the subject of the equation, A,T and rho are constants.
Simplify it as g(x) = u - floor(u). This function is then periodic with period 1, which makes your function periodic with period T, and thus it has no global inverse. rho just moves the function around horizontally and A scales it vertically. So your function is invertible on any interval of length T, and you can add z*T to the inverse to get another solution, where z is some integer. A simple inverse for g is g-1(v) = v, where the interval is [0, 1). For your function, you would choose an interval like [0, T) and the inverse on this interval would just be the inverse of f(x) = A(x/T + rho) which is f-1(y) = T(y/A - rho).
 
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  • #6
So it is
f(x) = A . frac(x/T + rho)​
with 'frac' representing the fractional part after disregarding the integer part.

As Halls points out, frac(1.87) = frac(2.87) = frac(3.87) ... = 0.87, so it is really not possible to get the original number back, starting from 0.87. Technically, the 'inverse' does not qualify as a function.

You could, however, define x = T . (y/A - rho + C), where C is any integer, and say that you have multiple solutions for the equation y = f(x), if this is useful.
 
  • #7
How did you guys see that so quickly? Amazing. God given gifts. Thanks for the help.
 
  • #8
They learned the definitions!
 

1. What is an inverse function?

An inverse function is a function that "undoes" the action of another function. In other words, if f(x) is a function, then its inverse, denoted as f-1(x), will return the original input x when applied to the output of f(x).

2. How do you find the inverse of a function?

To find the inverse of a function, you can follow these steps:

  1. Replace the function notation f(x) with y.
  2. Swap the x and y variables. This means that all instances of x in the original function become y, and all instances of y become x.
  3. Solve the resulting equation for y in terms of x.
  4. Replace y with f-1(x) to get the inverse function.

3. What is the difference between finding the inverse of a regular function and a function with a floor?

When finding the inverse of a regular function, you can simply follow the steps outlined in question 2. However, when dealing with a function with a floor, you must be careful to consider the domain of the function and the range of the inverse function. This is because the floor function (denoted as ⌊x⌋) rounds down to the nearest integer, which can affect the input and output values of the function and its inverse.

4. Are there any tips or tricks for finding the inverse of a function with a floor?

One helpful tip is to plot the original function and its inverse on a graph to visually see the relationship between the two. Other tricks include using the properties of the floor function, such as ⌊x⌋ = x - {x}, where {x} represents the fractional part of x, to simplify the inverse function.

5. How can finding the inverse of a function with a floor be used in real-life applications?

The concept of inverse functions with a floor can be applied in various fields, such as economics, physics, and computer science. For example, in economics, the inverse of a cost function can be used to determine the minimum price that a company should charge for a product in order to break even. In computer science, the inverse of a hash function with a floor can be used to retrieve the original data from a hashed value.

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