Do limit and differential operators commute?

In summary, the conversation discusses whether the equation lim_{x\to0} [d/dy d/dx f(x,y)] = d/dy [lim_{x\to0} d/dx f(x,y)] holds true for all functions f(x,y). The speaker believes this is true if the mixed partial derivatives of f(x,y) are continuous at x=0 and any y-value. They also mention a resource that discusses second-order partial derivatives and their applications. The questioner asks if they are trying to prove this equation, but the speaker clarifies that they are not, as differentiating with respect to both variables can be a hassle compared to differentiating by x, setting the limit, and then differentiating by
  • #1
2sin54
109
1
In general I'm wondering if

[tex]\lim_{x\to0} \left[\frac{d}{dy} \frac{d}{dx} f(x,y)\right] = \frac{d}{dy} \left[\lim_{x\to0} \frac{d}{dx} f(x,y)\right][/tex]

holds true for all f(x,y). Thanks.
 
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  • #2
I think this is true provided the mixed partial derivatives of function f(x,y) are continuous at x=0 and whatever y=value.

http://www.math.ucsd.edu/~mradclif/teaching/Math10C/LectureNotes/second_order_partial_derivatives.pdf

Are you trying to prove this?
 
  • #3
jedishrfu said:
I think this is true provided the mixed partial derivatives of function f(x,y) are continuous at x=0 and whatever y=value.

http://www.math.ucsd.edu/~mradclif/teaching/Math10C/LectureNotes/second_order_partial_derivatives.pdf

Are you trying to prove this?
No, not exactly. My f(x,y) is a huge compound function and it's a hassle to differentiate with respect to both variables and then take the limit, as opposed to differentiating by x, setting the limit and then differentiating (the now simpler function) by y.
 

1. What is the definition of a limit operator?

A limit operator is a mathematical operator that represents the limit of a function as its input values approach a certain value or point. It is denoted by the symbol "lim" and is commonly used in calculus.

2. What is a differential operator?

A differential operator is a mathematical operator that represents the derivative of a function. It is denoted by symbols such as "d/dx" or "∂/∂x" and is also commonly used in calculus.

3. What does it mean for two operators to commute?

Two operators commute if their order of operation does not affect the final result. In other words, if the two operators can be interchanged without changing the outcome, then they are said to commute.

4. Do limit and differential operators always commute?

No, limit and differential operators do not always commute. The order of operation can affect the final result, especially when considering more complex functions.

5. How can I determine if two operators commute?

To determine if two operators commute, you can try interchanging their order of operation and see if the result changes. If the result remains the same, then the operators commute. However, this may not be applicable for all cases, especially for more complex functions.

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