I've seen some problems where the OP writes integrals in this form
$\int {dt} f\left( t \right)$
or for double integrals
$\int {dx} \int {dtf\left( {t,x} \right)} $
Do they represent another kind of integrals, or is it just notation?
I've seen some problems where the OP writes integrals in this form
$\int {dt} f\left( t \right)$
or for double integrals
$\int {dx} \int {dtf\left( {t,x} \right)} $
Do they represent another kind of integrals, or is it just notation?
This is just notation. In general, $\int f(t) dt = \int dt f(t)$
In fact you can move the $dt$ term anywhere you want--as long as it remains within its corresponding integral. So $\int dx \int dt f(t, x) = \int \left( \int f(t, x) dt \right) dx = \int \int f(t, x) dt dx.$
However, $\int dx\,dt \color{red}{\int f(t, x)} \neq \int \int f(t, x) \, dt \, dx$
because on the LHS, the right integral in the red has no $d$ term and thus is nonsense.