Differentiable Greatest Integer Function

In summary, the function k(x) is differentiable for all real numbers except when x=0, where it is discontinuous. The derivative of k(x) can be found using the equation f'(x) = 2xk, where k=[1/x].
  • #1
kolley
17
0

Homework Statement


k(x)=x2*[1/x] for 0<x≤1
k(x)=0 for x=0
Find where k(x) is differentiable and find the derivative

Homework Equations


The Attempt at a Solution


I know that it is differentiable for all ℝ\Z on (0,1], but I am unsure how to find the derivative for this problem.
 
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  • #2
kolley said:

Homework Statement


k(x)=x2*[1/x] for 0<x≤1
k(x)=0 for x=0
Find where k(x) is differentiable and find the derivative

Homework Equations





The Attempt at a Solution


I know that it is differentiable for all ℝ\Z on (0,1], but I am unsure how to find the derivative for this problem.

If you mean what R\Z usually means then R\Z on (0,1] is (0,1). I suspect you mean something else. Suppose 1/x is between two integers, say n<1/x<n+1?
 
  • #3
Yes sorry that was a typo, should be (0,1). So would I set k=[1/x], which would make f(x)=x2*k

which would imply that f'(x)=2xk
Is this what you mean?
 
  • #4
kolley said:
Yes sorry that was a typo, should be (0,1). So would I set k=[1/x], which would make f(x)=x2*k

which would imply that f'(x)=2xk
Is this what you mean?

Sure. So if 1/x is between two integers then your function is differentiable, yes? Suppose 1/x is equal to an integer? Then what?
 
  • #5
If it's equal to an integer then it would not be differentiable.
 
  • #6
kolley said:
If it's equal to an integer then it would not be differentiable.

Why not? You have to give reasons.
 
  • #7
Because it's discontinuous at all integers.
 
  • #8
kolley said:
Because it's discontinuous at all integers.

True if you mean f(x) is discontinuous when 1/x is an integer. You should probably say that in a more proofy way, like saying what the one sided limits are of f(x) or using a theorem. But I think the main point of the exercise is what happens at x=0, since they bothered to define f(0)=0. f(x) might have a one-sided derivative at x=0. Does it?
 
Last edited:

Related to Differentiable Greatest Integer Function

What is the Differentiable Greatest Integer Function?

The Differentiable Greatest Integer Function, also known as the floor function, is a mathematical function that rounds down a given real number to the nearest integer. It is denoted by ⌊x⌋ or [x].

Is the Differentiable Greatest Integer Function continuous?

No, the Differentiable Greatest Integer Function is not continuous. It has a jump discontinuity at every integer value, as the function abruptly changes from one integer to the next.

What is the derivative of the Differentiable Greatest Integer Function?

Since the Differentiable Greatest Integer Function is not continuous, it does not have a derivative in the traditional sense. However, it can be approximated by a piecewise function using the difference quotient.

How is the Differentiable Greatest Integer Function used in real life?

The Differentiable Greatest Integer Function is often used in computer programming to truncate decimal numbers and to simulate rounding down in calculations. It is also used in economics and finance to model discrete changes in quantities.

What are the properties of the Differentiable Greatest Integer Function?

The Differentiable Greatest Integer Function is a non-increasing function, meaning that as the input increases, the output decreases or remains the same. It is also a step function, with a constant value between integers. Additionally, it is a discontinuous function with infinitely many jump discontinuities.

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