First of all I want to create a list of evenly spaceed points in a cubic region in $mathbb{R}^3$. Then I want to keep the points in this list which satisfy a certain condition, i.e. a function that takes these points in $mathbb{R}^3$ and outputs true or false depending on the details of my problem. Then I need to plot these points using some sort of a interpolation function, which will be able to show the surface that bounds the volume that the points in my list are located in.

The selection criterion is the following:

There is a matrix $mathcal{M}=mathcal{M}(x,y,z)$ defined for every point in this list. Say for the point $P= (1,4,5)$, the matrix $mathcal

{M}(1,4,5)$ is Positive Semi-Definite, then I want to **KEEP** the point $(1,4,5)$. If at that point the matrix is nott Positive Semi-Definite, then I want to **DISCARD** that point.

My problem is

- I could not create a list comprised of evenly spaced points in $mathbb{R}^3$.
- I could not discard or keep the elements of a given set based on the output that an element of the list gives when inputed into a function.
- I could not create a smooth surface which bounds a list of points in $mathbb{R}^3$.

Basically If at a point the matrix is positive semi-definite, then I want to keep that point. If at a point the matrix is not positive semi-definite, then I want to discard that point.

If needed I can also provide my function, which is the criteria for keeping or discarding certain points, but I am afraid it will only serve to clutter the discussion.