# Tagged Questions

**2**

votes

**1**answer

100 views

### Projection onto $\ell^{2,1}$ ball

Does anyone have an idea how to project onto the $\ell^{2,1}$ ball efficiently, i.e. how to solve
$$ u = \arg \min_u \|u-f \|^2 \text{such that } \left(\sum_i \big(\sum_j |u_{i,j}|\big)^2 ...

**2**

votes

**0**answers

64 views

### Variational problem for optimal weight function leading to shorter intervals with many primes

The motivation for the following problem stems from the recent preprint by James Maynard, see also Proposition 5 of the recent blogpost by Terrence Tao. The solution of this problem could give better ...

**2**

votes

**0**answers

63 views

### Approximating solutions to minima of the discrete Lagrangian

I have been stuck on this problem for a week and I'm not sure whether or not it is hard or I'm just missing something obvious.
General gist of the problem
I have a variational problem on a ...

**3**

votes

**1**answer

351 views

### Approximating functions in $H_0^1(\Omega)$ by piecewise affine ones.

I'm trying to understand how one approximates functions in $H_0^1(\Omega)$ by piecewise affine functions. The normal construction I have seen begins by breaking up your domain $\Omega$ into cubes ...

**4**

votes

**2**answers

1k views

### Minimizing a function containing an integral

I am trying to optimize a function of the following form:
$L = \int_{t=0}^{T}(AR-x)dt$, where A is a system parameter
i.e. I am trying to find the optimum x(t) that minimizes L over all admissible ...