I received an unexpected call from HR. I believe they completed the first, non-technical part of the interview during that call. I wasn't even awake when they called!

The technical interview is scheduled for roughly one week after that call. The phone interview was conducted by one engineer. Webex was prepared but never used. I suspect I wasn't qualified enough to advance to that stage.

Some of the questions I recall include:

• Calculate the eigenvalue of a matrix.
• Determine if the limit exists for a piecewise function.
• What is the possible value of a function at 'a' given the value and first-order derivative at 'b'?
• Rank of a matrix.
• Controllable canonical form from a transfer function.
• PID control.
• Position control in an open-loop system.
• Bode diagram, phase margin.
• Stability (mathematical proof).
• How to save variables using a mat file.
• Difference between break and continue.
• Difference between a script and a function.
• How objects are passed in Java: by value or by reference.
• Can you force garbage collection in Java?
• Pointers.
• Recursive methods.

Should be easy for a controls engineer.