Integration Symbol with Limits

Question

How can I write the integration symbol in latex as shown in the picture?

Answer 1

\documentclass{article}
\usepackage{amsfonts,amsmath}
\begin{document}
\[
  \int_{\substack{a\\\mathcal{P}}}^b (\nabla ...)
\]

\[
  \int\limits_{\substack{a\\\mathcal{P}}}^b (\nabla ...)
\]
\end{document}

Answer 2

Not a symbol I would use; but here it is, with a definition that allows easier syntax and detaches the “P” from the lower limit:

\documentclass{article}
\usepackage{mathtools}

\newcommand{\Pint}{%
  \mathrlap{\mathop{\phantom{\int}}\limits_{\!\mathcal{P}}}%
  \!\int
}

\begin{document}
\[
\int_{\mathbf{a}}^{\mathbf{b}}
\Pint_{\mathbf{a}}^{\mathbf{b}}
\]
\end{document}

The first \int is just for comparing the placement of symbols.

Answer 3

A reasonably accurate reproduction of the screen shot you posted is shown below.

Note the use of \mathbf for a and b, the use of \mathcal for P, the "invisible" first row in the \substack to push the entire lower-limit group down a bit, and the \! (negative thinspace) directive in front of \substack to move the lower-limit group a bit to the left:

\documentclass{article}
\usepackage{amsmath,amsfonts}
\begin{document}
\[
\int_{\!\substack{\phantom{x}\\ \mathbf{a}\\ \mathcal{P}}}^{\mathbf{b}} 
\]
\end{document}

If you're not interested in a literal copy of the screen shot you posted but just in how to enter an integral symbol with limits, you could get by with writing

\int_{<lower limit>}^{<upper limit>}

Answer 4

Some attempts using \underset:

\documentclass{article}
\usepackage{amsmath}
\begin{document}
\huge
\[
\mathbf{
\underset{\mathcal{P}}{\phantom{P}\int_{\!a}^{b}} 
\underset{\mathcal{P}}{\int_a^b}
\underset{\!\mathcal{P}}{\int_{\!a}^{b}} 
\int_{\!\underset{\mathcal{P}}a}^b 
\intop_{\underset{\mathcal{P}}{a}}^{b}
}\]
\end{document}

Answer 5

The key problem of the OP here is to stack the subscript \rho (the weird P) UNDER subscript a. To achieve this, use the command \substack as demonstrated below in the MWE:

\documentclass{article}
\usepackage{amsmath}
\begin{document}
\begin{equation}
  \int_{\substack{
            a\\
            \rho}}^b
     (\bigtriangledown
\end{equation}
\end{document}