Help with Notation: Understanding x(.) & C(.)

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In summary, the dot notation, such as x(.) or C(.), is used to indicate a function where the specific argument is not specified or can vary. It is a way of saying "x is a function of an unspecified argument" or "C is a function of any argument". This notation is commonly used in mathematics and can represent functions with multiple variables or even functions of functions.
  • #1
emergentecon
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Having trouble understanding some notation:

x(.) or C(.) (the dot is in fact in the center i.e mid-way vertically in the brackets).

I have never run into this before? What does it mean if x is a function of "."?
 
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  • #2
emergentecon said:
Having trouble understanding some notation:

x(.) or C(.) (the dot is in fact in the center i.e mid-way vertically in the brackets).

I have never run into this before? What does it mean if x is a function of "."?
More context please.
 
  • #3
haruspex said:
More context please.
Apologies, I thought it was something along the lines of f' being the first derivative of the function, and nothing else (to my knowledge).

And I quote "C(.) is a choice rule (technically a correspondence) that assigns a nonempty set of chosen elements C(β) ⊂ β for every budget set β ∈ B."
 
  • #4
emergentecon said:
Apologies, I thought it was something along the lines of f' being the first derivative of the function, and nothing else (to my knowledge).

And I quote "C(.) is a choice rule (technically a correspondence) that assigns a nonempty set of chosen elements C(β) ⊂ β for every budget set β ∈ B."
Seems like it is just a way of saying "C is a function".
 
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  • #5
haruspex said:
Seems like it is just a way of saying "C is a function".
Ok, thanks!
 
  • #6
haruspex said:
Seems like it is just a way of saying "C is a function".
Someone has mentioned to me that it indicates that a function can only take a single argument . . . without specifying the specific argument?
Not sure if this is true.
 
  • #7
emergentecon said:
Having trouble understanding some notation:

x(.) or C(.) (the dot is in fact in the center i.e mid-way vertically in the brackets).

I have never run into this before? What does it mean if x is a function of "."?

I got a formal answer:

f(.) means that we have a univariate (one variable) function.
The difference between f(x) and f(.) is that that, f(x) denotes a univariate function depending from the specific one-variable x, whilst f(.) denotes an one variable function depending from any one-variable we like.
We can write, for instance, f(x) or f(y) or f(z) etc
 
  • #8
emergentecon said:
I got a formal answer:

f(.) means that we have a univariate (one variable) function.
The difference between f(x) and f(.) is that that, f(x) denotes a univariate function depending from the specific one-variable x, whilst f(.) denotes an one variable function depending from any one-variable we like.
We can write, for instance, f(x) or f(y) or f(z) etc

Be very careful about what you regard as a "variable". I have seen functions C(.) whose arguments are n-vectors, so we really have ##C(x_1,x_2, \ldots x_n)##, but with the n arguments bundled together into a single "vector" ##\vec{x} = (x_1,x_2 \ldots,x_n)##. In that sense, C is a function of the single "variable} ##\vec{x}##. I have also seen functions C(.) whose arguments are functions themselves (such things are usually called functionals), so in a sense are functions of infinitely many variables. But, again, these several variables are all bundled together into a single object ##x(.)##, and that is plugged into the formula for C.
 
  • #9
The dot notation is often used when you want to define a function from one that's already defined, without coming up with a new function symbol. For example, if ##f:\mathbb R^2\to\mathbb R## and ##y\in\mathbb R##, then ##f(\cdot,y)## denotes the function ##x\mapsto f(x,y)## with domain ##\mathbb R##, i.e. the function ##g:\mathbb R\to\mathbb R## such that ##g(x)=f(x,y)## for all ##x\in\mathbb R##. So for all ##x\in\mathbb R##, we have ##f(\cdot,y)(x)=f(x,y)##. The dot is just telling you where to put the "input".
 

FAQ: Help with Notation: Understanding x(.) & C(.)

1. What does x(.) and C(.) represent in notation?

In notation, x(.) typically represents a variable, while C(.) represents a constant. This means that the value of x can change, while the value of C remains the same.

2. How is x(.) different from x?

The notation x(.) indicates that x is a function, while x without the parentheses is simply a variable. In other words, x(.) represents the entire function, while x represents a specific value or input of that function.

3. Can C(.) be a function as well?

Yes, C(.) can represent a function, but it typically represents a constant in mathematics. This means that the value of C remains the same regardless of the input or the value of x.

4. What is the purpose of using x(.) and C(.) in equations?

x(.) and C(.) are used in equations to represent the variables and constants that make up the equation. This allows for a more concise and standardized way of expressing mathematical concepts and formulas.

5. How do I know when to use x(.) and when to use C(.) in an equation?

In most cases, x(.) is used to represent a variable that can change, while C(.) is used to represent a constant that remains the same. However, the use of x(.) and C(.) can vary depending on the context and the specific equation being used.

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