- #1
johann1301
- 217
- 1
Are the Real numbers R a subset of the complex numbers C?
WWGD said:Each of C, R have different structure ; as sets, as fields, as metric spaces, etc. If you consider both as sets, then yes; R is a subset of C, it is the subset of the form {a+i.0: a is a Real number}. But there are relationships between the two other than this one.
haruspex said:As Halls and FactChecker point out, it's a lot stronger than merely being a subset in the set-theoretic sense. (In fact, in that sense, it's a matter of choice whether you consider it a subset, or even which subset!)
The point is that all the structure of C, as inherited by the subset we think of as R, is an exact match for the structure of R. The dyadic etc. operations all still work and produce the 'right' answers. In short, it is an isomorphism, which is as close as you can get to saying two independently defined mathematical entities are the 'same'.
homeomorphic, as it happens, I've just been arguing on another thread against thinking of C as being R2 with some multiplication rules. That's fine for a visualisation, but it can convey the impression that C is some sort of two dimensional vector space. This gets quite confusing when later you find C is a scalar field over which vector spaces can be defined.
johnqwertyful said:But C IS a 2 dimensional vector space over R. All field extensions are vector spaces over their base fields.
haruspex said:No, it induces a 2D vector space, but it is not the same as a 2D vector space. Part of the definition of C is the multiplication function *:CxC→C.
haruspex said:As Halls and FactChecker point out, it's a lot stronger than merely being a subset in the set-theoretic sense. (In fact, in that sense, it's a matter of choice whether you consider it a subset, or even which subset!)
The point is that all the structure of C, as inherited by the subset we think of as R, is an exact match for the structure of R. The dyadic etc. operations all still work and produce the 'right' answers. In short, it is an isomorphism, which is as close as you can get to saying two independently defined mathematical entities are the 'same'.
homeomorphic, as it happens, I've just been arguing on another thread against thinking of C as being R2 with some multiplication rules. That's fine for a visualisation, but it can convey the impression that C is some sort of two dimensional vector space. This gets quite confusing when later you find C is a scalar field over which vector spaces can be defined.
I fail to see why that would be confusing. C is naturally endowed with a real 2-dimensional Vector space structure, ans also with a field structure (thus a complex 1-dimensional vector space structure).
Therodre said:Hi,
I fail to see why that would be confusing. C is naturally endowed with a real 2-dimensional Vector space structure, ans also with a field structure (thus a complex 1-dimensional vector space structure).
Although i would not say that two isomorphic structure are as close as it gets to being the same, i'd say that what is closest is "uniquely isomorphic" (which is the case in the situation you're referring to) which can happen for any construction of C if you work with fields (that are R algebras) with one marked element.
I don't think this is correct. I bet we can come up with examples of things that are perfectly well defined but are not even uniquely isomorphic to themselves. Isn't the complex plane isomorphic to itself by the identity mapping and also by the mapping of each number to its conjugate? In fact, any nontrivial automorphism will probably be a good example. An isomorphism is enough to call things identical, unique or not.Therodre said:but to satisfy a universal property you already need to be unique up to unique isomorphism
FactChecker said:I don't think this is correct. I bet we can come up with examples of things that are perfectly well defined but are not even uniquely isomorphic to themselves. Isn't the complex plane isomorphic to itself by the identity mapping and also by the mapping of each number to its conjugate? In fact, any nontrivial automorphism will probably be a good example. An isomorphism is enough to call things identical, unique or not.
economicsnerd said:I have to wonder whether this discussion is the right one for clarifying the OP's question.
micromass said:In the case that the OP is still following the thread for all intents and purposes, yes ##\mathbb{R}## is a subset of ##\mathbb{C}##. So unless you're doing some advanced course like analysis or set theory, this is the right answer to your question. And even if you do the advanced course, the answer would still be morally right in my opinion. You can forget the rest of the answers in this thread which will likely be confusing and just take the answer that ##\mathbb{R}\subseteq \mathbb{C}## is true.
Matterwave said:A question of notation here. Why not say ##\mathbb{R}\subset\mathbb{C}## instead of using the symbol ##\subseteq##?
Matterwave said:A question of notation here. Why not say ##\mathbb{R}\subset\mathbb{C}## instead of using the symbol ##\subseteq##?
Real numbers are numbers that can be represented on a number line and include both positive and negative numbers, as well as fractions and decimals. Complex numbers, on the other hand, include a real part and an imaginary part and are typically written in the form a + bi, where a and b are real numbers and i is the imaginary unit.
Yes, real numbers are a subset of complex numbers. This means that all real numbers can also be represented as complex numbers with 0 as the imaginary part.
No, complex numbers cannot be graphed on a number line because they have both real and imaginary components. They are typically graphed on a complex plane, with the real numbers represented on the horizontal axis and the imaginary numbers on the vertical axis.
Imaginary numbers are included in the complex number system to allow for solutions to certain equations that cannot be solved with real numbers alone. They also have many applications in fields such as engineering, physics, and economics.
Yes, real numbers and complex numbers can be added and multiplied together. When adding or multiplying a real number and a complex number, the real number is simply added or multiplied to the real part of the complex number, while the imaginary part remains unchanged.