# Calculation of path integral in QFT

I am studing QFT using the text book of Srednicki's. And I am stuck on one of calculations of the integrals in his book.

Consider a harmonic oscillator with hamiltonian:

We can write the following integral for the transition from ground state to ground state:

In his book, he said: Passing to the lagrangian formulation then gives:

What does he mean by passing to the lagrangian formulation? And how did he calculate the $$Dp$$ part?

It's on page 46 of the book: http://chaosbook.org/FieldTheory/extras/SrednickiQFT03.pdf

For some reason he left out the $$hp$$ term in the second equation you quoted. If you put it back as it is in the earlier sections, and then do the $$p$$ inetegrals you get the $$(m/2)(\dot q+h)^2$$ term directly.