Hi(adsbygoogle = window.adsbygoogle || []).push({});

I've got a question about a term in a formula I've found in Mandl&Shaw's QFT book

It's about equation 2.18 on page 31

[tex] L(t) = {\sum_i \delta \bf{x}_i {\cal L}_i \ ... [/tex]

Why is there a delta x_i when summing over all lagrangians for getting the lagrange-function for the whole system?

And what operator is that delta in this particular equation?

The difference between two different points? (wouldn't that rather be [tex] \Delta \bf{x} [/tex] ?)

[tex] \delta [/tex] serves only as functional derivative AFAIK

**Physics Forums | Science Articles, Homework Help, Discussion**

Dismiss Notice

Join Physics Forums Today!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

# Explanation for term in formula, QFT

**Physics Forums | Science Articles, Homework Help, Discussion**