In the current version of Octave the standard syntax
for this kind of operation is of the form:
object = class_method (object, method_arguments)
I would instead leave interpolate as it is. Basically my point is that in the future, when classdef will make it to the stable version, a call like the one up here could just leave the return object aside and work as its C++ counterpart. Probably the problem
here is that I am too zealous in trying to stay close to the original FEniCS interface, if you deem the other approach more convenient I will adapt and code accordingly.