# Strange integral of heaviside step function

I ran across this integral while reading Ashcroft and Mermin's solid state physics book....

∫Θ(f - f(t) )dt = t_max - t_min

Where Θ is the heaviside step function and the integral runs from 0 to infinity.

Does anyone have any idea how this integral makes sense?

## Answers and Replies

Mark44
Mentor
I ran across this integral while reading Ashcroft and Mermin's solid state physics book....

∫Θ(f - f(t) )dt = t_max - t_min

Where Θ is the heaviside step function and the integral runs from 0 to infinity.

Does anyone have any idea how this integral makes sense?
Can you post a picture of the page that shows this integral?