Numerical analysis: I had the students run a “5 step predictor, 4 step corrector, variable step size” routine to solve a differential equation. This was a homework problem.
A student reported that the routine failed.
So, I looked at it…the interval for the solution was and the initial step size was…. and what is 5 times .05? Yep, the correction part overshot the right endpoint and the “next h” was indeed negative.
This came to me when I was eating dinner…and sure enough..
OMG, I am an idiot. 🙂