Why Do Functions Have Only One Output for Each Input?

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Discussion Overview

The discussion revolves around the definition of functions in mathematics, specifically why functions are characterized by having only one output for each input. Participants explore the implications of this definition and the distinction between functions and other types of relations.

Discussion Character

  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • Some participants question why functions are defined to have only one output for each input, using examples like circles to illustrate cases where multiple outputs exist for a single input.
  • Others argue that functions are a special type of relation, which inherently have only one possible output for each input, making them more useful in certain contexts.
  • A participant mentions that in practical scenarios, such as determining the position of an object over time, the one-to-one relationship of functions is beneficial.
  • There is a suggestion that the distinction between functions and relations is important, particularly when considering cases where multiple outputs may be possible.

Areas of Agreement / Disagreement

Participants express differing views on the necessity and implications of the distinction between functions and relations. No consensus is reached regarding the broader usefulness of functions versus relations.

Contextual Notes

Participants do not fully explore the underlying assumptions about the definitions of functions and relations, nor do they address potential exceptions or variations in these definitions.

Rishabh Narula
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Why do we define functions as only
as only those graphs which have
only one y value for each x value.
for eg. we don't say that a circle
is a graph of a function,because
its graph would have two y values
for same x values.
what i mean to ask is why not call
anything that takes a input and gives
an output a function?Why this distinction?
 
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Rishabh Narula said:
Why do we define functions as only
as only those graphs which have
only one y value for each x value.
for eg. we don't say that a circle
is a graph of a function,because
its graph would have two y values
for same x values.
what i mean to ask is why not call
anything that takes a input and gives
an output a function?Why this distinction?

The question is really why are functions so useful? There are a lot of examples where what we want to study is something that has a definite value. The position of an object at time ##t## is a function of ##t##.

The function represents this relationship of one input, one output, which is very useful.
 
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Rishabh Narula said:
what i mean to ask is why not call
anything that takes a input and gives
an output a function?Why this distinction?
Because we have already have a name for it. They are called a relation. Functions are special relations with only one possible y value. It's easy to see that this is more useful than a relation. If you compute the square root of a number, then your algorithm will only give you one solution, not both. If we drive from A to B, we will be at only one place at time T, not two; etc. And as I said: in case we are interested in a one to many relation, we will call it a relation. We have a name.
 
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Rishabh Narula said:
why not call
anything that takes a input and gives
an output a function?
I guess you mean "a choice of outputs" because that is what your example of the circle does.
Why this distinction?
Because it is important to distinguish between the case where it gives a single output from the case where it gives a choice of multiple outputs.
 

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