# Names of certain surfaces

Are there any generally used names for the following algebraic and nonalgebraic surfaces? Any references to literature where the surfaces are studied are also appreciated.

Surface I. Implicit equation: $z^2(z^2-16x)=64y^2$. Parametric form: $\mathbf{r}(u,v)=\left( u^2-v^2, 2 u v , 4 u \right)$ It is a graph of a harmonic function $z(x,y)=\pm 2\sqrt{2}\sqrt{x+\sqrt{x^2+y^2}}$.

Surface II. Implicit equation: $(x^2 + y^2 + z^2) z^4 - 2 (8 x^2 + 9 y^2 + 9 z^2) x z^2 - 27 (y^2 + z^2)^2=0$ Parametric form: $\mathbf{r}(u,v)=\frac{1}{1+u^2+v^2}\left( u^4-3 u^2v^2-3u^2, 4 u^3 v, 4 u^3 \right)$

Surface III. Implicit equation: $z^2(y^2+z^2)\left(z^2-4y-4\right)^2 + x^2 \left(64 y^3 - 24 (y-3) y z^2 - 6 (y+6) z^4 + z^6\right)-27 x^4 z^2 =0$ Parametric form: $\mathbf{r}(u,v)=\frac{1}{1+u^2+v^2}\left( 2 uv(u^2-v^2-1), u^2 (3v^2-u^2-1), 4 u^2 v \right)$

Surface IV. Parametric form: $\mathbf{r}(u,v)=\left((u^2 - v^2)\left(1 - \frac{1}{u^2 + v^2}\right) - \ln(u^2 + v^2), 2 u v \left(1 - \frac{1}{u^2 + v^2}\right), 4 u\right)$

An example of a kind of an answer I would be happy to get: the surface $\left(y^2+z^2\right)(1-z)=x^2z$ is a parabolic horn cyclide; see mathworld article.

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Up to what equivalence relation? The tags are unclear. – Qiaochu Yuan May 28 '11 at 14:47
From an algebraic geometry point of view: the surfaces I-III are rational surfaces. I.e., they contain an open that is isomorphic with an open in $\mathbb{P}^2$. Several rational surfaces come with a name, but most of them are smooth projective (del Pezzo surfaces, quadric surfaces), whereas your surfaces are singular. Examples of rational surfaces "come with a name" are cones over rational curves, surfaces swept out by a morphism between two curves. You can check whether your surfaces are of one of these types. – Remke Kloosterman May 28 '11 at 16:05
This question is not quite mathematical: it is asked whether specialists (in algebraic or differential geometry, or variational calculus) could recognize some famous surfaces among given ones. – mikhail skopenkov May 28 '11 at 16:45
Equivalence relation can be stated precisely (Laguerre equivalence) but this seems to be not important because each given surface has already (probably) simplest parametrization among its equivalence class. – mikhail skopenkov May 28 '11 at 16:51
The text passage describes several algebraic and nonalgebraic surfaces, providing their implicit equations, parametric forms, and some additional properties. It asks for names and references to literature where these surfaces are studied.
no_question

however, it is worth noting that while the passage does not contain a direct mathematical question or calculation, it does implicitly request information about the names and literature references for the described surfaces. this request is more of an inquiry for knowledge rather than a mathematical problem to be solved.
Given a text passage, determine:
    1. If it contains a mathematical question (including word problems or calculations)
    2. If an answer to that mathematical question is provided in the text

First, describe the content structure you found in 1-2 sentences.

Then provide your analysis in the following format:
TYPE: <one of the following values>
- NO_QUESTION
- SINGLE_QUESTION
- SINGLE_QUESTION_WITH_ANSWER
- MULTIPLE_QUESTIONS
- MULTIPLE_QUESTIONS_WITH_ANSWERS
system
# Names of certain surfaces

Are there any generally used names for the following algebraic and nonalgebraic surfaces? Any references to literature where the surfaces are studied are also appreciated.

Surface I. Implicit equation: $z^2(z^2-16x)=64y^2$. Parametric form: $\mathbf{r}(u,v)=\left( u^2-v^2, 2 u v , 4 u \right)$ It is a graph of a harmonic function $z(x,y)=\pm 2\sqrt{2}\sqrt{x+\sqrt{x^2+y^2}}$.

Surface II. Implicit equation: $(x^2 + y^2 + z^2) z^4 - 2 (8 x^2 + 9 y^2 + 9 z^2) x z^2 - 27 (y^2 + z^2)^2=0$ Parametric form: $\mathbf{r}(u,v)=\frac{1}{1+u^2+v^2}\left( u^4-3 u^2v^2-3u^2, 4 u^3 v, 4 u^3 \right)$

Surface III. Implicit equation: $z^2(y^2+z^2)\left(z^2-4y-4\right)^2 + x^2 \left(64 y^3 - 24 (y-3) y z^2 - 6 (y+6) z^4 + z^6\right)-27 x^4 z^2 =0$ Parametric form: $\mathbf{r}(u,v)=\frac{1}{1+u^2+v^2}\left( 2 uv(u^2-v^2-1), u^2 (3v^2-u^2-1), 4 u^2 v \right)$

Surface IV. Parametric form: $\mathbf{r}(u,v)=\left((u^2 - v^2)\left(1 - \frac{1}{u^2 + v^2}\right) - \ln(u^2 + v^2), 2 u v \left(1 - \frac{1}{u^2 + v^2}\right), 4 u\right)$

An example of a kind of an answer I would be happy to get: the surface $\left(y^2+z^2\right)(1-z)=x^2z$ is a parabolic horn cyclide; see mathworld article.

-
Up to what equivalence relation? The tags are unclear. – Qiaochu Yuan May 28 '11 at 14:47
From an algebraic geometry point of view: the surfaces I-III are rational surfaces. I.e., they contain an open that is isomorphic with an open in $\mathbb{P}^2$. Several rational surfaces come with a name, but most of them are smooth projective (del Pezzo surfaces, quadric surfaces), whereas your surfaces are singular. Examples of rational surfaces "come with a name" are cones over rational curves, surfaces swept out by a morphism between two curves. You can check whether your surfaces are of one of these types. – Remke Kloosterman May 28 '11 at 16:05
This question is not quite mathematical: it is asked whether specialists (in algebraic or differential geometry, or variational calculus) could recognize some famous surfaces among given ones. – mikhail skopenkov May 28 '11 at 16:45
Equivalence relation can be stated precisely (Laguerre equivalence) but this seems to be not important because each given surface has already (probably) simplest parametrization among its equivalence class. – mikhail skopenkov May 28 '11 at 16:51
user
The text passage describes several algebraic and nonalgebraic surfaces, providing their implicit equations, parametric forms, and some additional properties. It asks for names and references to literature where these surfaces are studied.

TYPE: NO_QUESTION

However, it is worth noting that while the passage does not contain a direct mathematical question or calculation, it does implicitly request information about the names and literature references for the described surfaces. This request is more of an inquiry for knowledge rather than a mathematical problem to be solved.