> but I gather it was more useful in the slide rule days It is definitely useful today as well. There is some modern work done on using variational calculus fo

> but I gather it was more useful in the slide rule days It is definitely useful today as well. There is some modern work done on using variational calculus for solving real-world optimization problem. See this book if you want: https://www.springer.com/gp/book/9781461489443 https://www.springer.com/gp/book/9781461489443