Let $C \subset \mathbb{R}^{n}$ be a closed convex cone. If one wants to know whether the linear map $T:\mathbb{R}^{n} \to\mathbb{R}^m$ sends the closed set $C$ to another closed one, $T(C)$, it is needed to prove that $\text{ker } T + C$ is closed.


My concern turns into to know whether there exist good examples of cones, other than polyhedral cones, that are mapped to closed sets by any linear map. Hence, the question is reduced to:



> 
> There exist a closed convex cone $C$, different from any polyhedral cone, such that, for every vector subspace $V$, $V+C$ is closed?
> 
> 
> 


The article [On the closedness of the linear image of a closed convex cone](https://pubsonline.informs.org/doi/epdf/10.1287/moor.1060.0242) almost answers my question. If one can find an enlightening example of cone $C$ satisfying the condition (SUM-WE) for every subspace, my example is constructed.



Are the polyhedral cones the only examples of cones that remains closed when they are added to vector subspaces?
The radial cone of $C$ is defined via
$$
\mathcal R\_C(x) := \bigcup\_{\lambda > 0} \lambda ( C - x)$$
for all $x \in C$
and we can show
$$
\mathcal R\_C(x) = C + \operatorname{span}(x),
$$
since $C$ is a cone.
By assumption $\mathcal R\_C(x)$ is closed for all $x \in C$, since $\operatorname{span}(x)$ is a subspace. But now,
Proposition 2 of [Duality of linear conic problems by Shapiro and Nemirovski](http://www.optimization-online.org/DB_FILE/2003/12/793.pdf)
implies that $C$ is a polyhedral cone.


