About the problem
Let \(u:\mathbb{R}^n\to\mathbb{R}\) be a real polynomial. Its graph in \(\mathbb{R}^{n+1}\) is minimal if and only if u solves the minimal surface equation
\[\operatorname{div}\left(\frac{\nabla u}{\sqrt{1+|\nabla u|^2}}\right)=0.\]This problem asks for a non-affine polynomial with \(n \geq 8\) and with real algebraic coefficients which is a solution to the minimal surface equation.
This problem, which was posed by Simon, is an algebraic version of the Bernstein problem.
If a solution to this problem exists, then it will be the first known example of a minimal surface that is the graph of a non-affine polynomial. (There are known non-affine solutions, but they are not polynomial.) A solution would ideally help us understand how to build minimal surfaces in high dimensions.
Prompt
Let u : R^n -> R be a real polynomial. The graph {(x, u(x)) : x in R^n} in R^(n+1) is a minimal
surface if and only if u solves the minimal surface equation
div( grad u / sqrt(1 + |grad u|^2) ) = 0.
Clearing the positive denominator, this is equivalent to the polynomial identity
F_u := (1 + |grad u|^2) * (Laplacian u) - sum_{i,j=1}^n u_i u_j u_ij == 0,
where u_i = du/dx_i, u_ij = d^2u/(dx_i dx_j), |grad u|^2 = sum_i u_i^2, and Laplacian u = sum_i u_ii.
Your task: find a non-affine polynomial u in R[x_1, ..., x_n] for some n >= 8 such that F_u is the
zero polynomial (equivalently, a polynomial u of total degree >= 3 with F_u == 0). Such a u would be
a polynomial entire minimal graph. Coefficients may be any real algebraic numbers.
Solution format:
* Write your answer to a JSON file and submit its path.
* The JSON must be an object with these keys:
- "n": the number of variables (an integer; must be at least 8).
- "coefficient_field": how the coefficients are given. Either
* the string "Q" (the rational numbers), in which case each "coeff" below is a single
rational string such as "3/2" or "-5"; or
* a number field object
{"type": "number_field",
"min_poly": ["a_0", "a_1", ..., "a_d"], # rational strings, low degree first:
# a_0 + a_1 T + ... + a_d T^d
"isolating_interval": ["a", "b"]} # rational strings with a < b
defining theta as the UNIQUE REAL root of min_poly in the open interval (a, b). min_poly
must be IRREDUCIBLE over Q and of degree >= 2, and (a, b) must bracket exactly one of its
real roots. Then theta is a real algebraic number and each "coeff" below is a LIST of
rational strings [c_0, c_1, ..., c_{m-1}] with m <= d, meaning c_0 + c_1*theta + ... .
- "polynomial": a list of terms, each {"coeff": <coeff>, "exp": [e_1, ..., e_n]}, representing
u(x) = sum over terms of coeff * x_1^e_1 * ... * x_n^e_n.
Each "exp" is a list of exactly n non-negative integers.
Example (illustrating the format only):
{
"n": 8,
"coefficient_field": {"type": "number_field", "min_poly": ["-2", "0", "1"],
"isolating_interval": ["1", "2"]},
"polynomial": [
{"coeff": ["0", "1"], "exp": [1, 0, 0, 0, 0, 0, 0, 0]},
{"coeff": ["3/2"], "exp": [0, 1, 0, 0, 0, 0, 0, 0]}
]
}
Here min_poly is T^2 - 2 and isolating_interval (1, 2) selects theta = +sqrt(2) (the interval
(-2, -1) would select -sqrt(2)), so this encodes u = sqrt(2)*x_1 + (3/2)*x_2.