Undefined value and Infinite value

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Discussion Overview

The discussion revolves around the concepts of undefined values and infinite values in the context of functions. Participants explore the relationship between these two concepts and seek clarification on their definitions and implications.

Discussion Character

  • Conceptual clarification, Debate/contested

Main Points Raised

  • Salil questions whether an undefined value at a particular time in a function necessarily implies that the value is infinite, and why undefined values are not simply referred to as infinity.
  • One participant asserts that infinite and undefined are different concepts, noting that while infinite values usually imply undefined, undefined values do not have to be infinite.
  • Another participant provides an example of the logarithm function, stating that it is negative infinity at zero (thus undefined) but is simply undefined for negative values of x without being infinite.
  • A further example is introduced regarding an empty function, which has no domain and does not involve infinity at all.
  • Another example is given with a piecewise function, where the function is explicitly undefined at zero.

Areas of Agreement / Disagreement

Participants generally agree that infinite and undefined values are distinct concepts, but there is no consensus on the implications of these definitions or the specific conditions under which a value is considered undefined or infinite.

Contextual Notes

Some assumptions about the definitions of functions and their domains may not be explicitly stated, and the discussion does not resolve the nuances of when a value is classified as undefined versus infinite.

salil87
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Hi
When we say that a function has an undefined value at a particular time does it mean it is infinite at that time? I mean most of the time it is infinite. But is an infinite value always called undefined and is an undefined value always infinite? If so why is it called undefined? Why not infinity?
Thanks
Salil
 
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Welcome to PF, salil87! :smile:

Infinite and undefined are different things.
For a function, infinite usually implies undefined.
But undefined does not have to be infinite.

For instance, the function log(x) is negative infinity at zero and as such undefined at zero.
But for negative values of x, log(x) is simply undefined (but not infinite).
 
for a slighty silly example, consider the empty function, which has no domain.

its graph is, of course, blank, but infinity doesn't even enter the picture.
 
Or: define f(x)= 3x for x> 0, f(x)= 2x for x< 0. Then f(0) is, literally, "undefined".
 
Thanks a lot. :-)

Thanks
Salil
 

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