Question

The reason behind the question

For a physics-project, we want to analyze two surfaces (specified by a bunch of vertices) and calculate the volume between those surfaces. To be able to do this, we want to implement a two-dimensional interval-search tree. In total the asymptotic run time, will be close to O(n²log n).

The question

In summary we are going to implement an algorithm, which will be quite time-expensive. Furthermore, the algorithm doesn’t profit from the highly optimized math libraries in matlab. Therefore, we are considering to call Java from matlab. Conclusively we would like to know:

"To what degree is Java faster than matlab, ignoring the highly optimized performance from the math libraries in matlab?"

and

"Is there any significant delay when repeatedly calling a java method from matlab?"

e.g. does the JVM have to be started every time the method is called? does the jar have to be loaded every single time the method is called?

I hope some of you could help me (and maybe others) with this question.

Answer 1

If you decide to write the implementation in MATLAB, here are some very good points @AndrewJanke made in an excellent answer regarding OOP performance in MATLAB (worth reading the whole post):

Mimicking a C++ or Java class in MATLAB probably won’t be optimal.
Java/C++ classes are typically built such that objects are the
smallest building blocks, as specific as you can (that is, lots of
different classes), and you compose them in arrays, collection
objects, etc, and iterate over them with loops. To make fast MATLAB
classes, turn that approach inside out. Have larger classes whose
fields are arrays, and call vectorized methods on those arrays.

The point is to arrange your code to play to the strengths of the
language – array handling, vectorized math – and avoid the weak spots.

To answer your questions, and I quote the documentation:

At MATLAB startup, part of the MATLAB virtual address space is
reserved by the Java Virtual Machine (JVM) and cannot be used for
storing MATLAB arrays.

so it is only initialized once at startup.

Also there is an overhead when calling Java methods as opposed to M-files (since MATLAB types have to be marshalled to and from Java data types).

Now if you want to squeeze out every last bit of performance, make sure to call Java methods as:

func(obj)

instead of:

obj.func()