The phrase "a rather complex problem" is correct and usable in written English.
You can use it when describing a situation or issue that involves multiple factors or is difficult to understand or solve.
Example: "The team is currently working on a rather complex problem that requires innovative solutions and collaboration."
Alternatives: "a quite intricate issue" or "a somewhat complicated challenge."
The modeling of thermal reaction furnaces of Sulfur Recovery Units (SRUs) is a rather complex problem since it involves different modeling scales such as the kinetic/molecular scale, the reactor scale, and the chemical process scale.
However, the optimized design of a heliostat field is a rather complex problem because the annual performance of a heliostat is a function of not only the instants of time considered and its own position, but also the relative location of neighbouring heliostats, which cause shadows and blockings.
This allows for a much more adaptable system, but it unfortunately is still a rather complex problem requiring a lot of compute.
This is a rather complex problem not discussed here, but left for a future work.
Generally, this is a rather complex problem, which depends on many factors including the geometry of the electrode as well as the distance and orientation of axons with respect to the electrode.
To solve this rather complex problem, we propose a novel object localization method by predicting object regions before extracting them.
However for moderate to large samples and from a programming point of view, this becomes a rather complex computational problem such that we would recommend either bootstrap or jackknife methodologies for the purpose of variance estimation.
For example, pain, depression, and delirium are subtle, rather complex problems to detect, particularly in populations with substantial impairments in cognition or communication.
The number of process variables and their interdependence in a pan coating process can make it a rather complex scale-up problem.
