My \mathcal{U} turns out to be curvy? (different than default) [duplicate]

Question

My preamble :

\documentclass[12pt,a4paper]{report}
\usepackage[lmargin=3.81cm,tmargin=2.54cm,rmargin=2.54cm,bmargin=2.52cm]{geometry}
\linespread{1.5}
\usepackage{amssymb}
\usepackage{ dsfont }
\usepackage{textcomp}
\usepackage{wrapfig}
\usepackage{array}
\usepackage{indentfirst}
\usepackage{colortbl}
\usepackage{float}
\usepackage{changepage}
\usepackage{longtable}
\usepackage{mathptmx}
\usepackage{color}
\usepackage{graphicx}
\usepackage{lettrine}
\usepackage{hyperref} 
\usepackage[nottoc,notlof,notlot]{tocbibind} % add to TOC
\usepackage{caption}

When I add the command :

 $\mathcal{U}$

I get

instead of

Can anyone tell me why is that happening ? and how to get the second U instead of my current one.

Answer 1

It's because you are loading mathptmx, which also changes the math fonts. If you want to keep the mathptmx package, but with the original \mathcal symbols, use

\DeclareMathAlphabet{\mathcal}{OMS}{cmsy}{m}{n}

A complete example:

\documentclass[12pt,a4paper]{report}
\usepackage{mathptmx}

\DeclareMathAlphabet{\mathcal}{OMS}{cmsy}{m}{n}

\begin{document}

$\mathcal{U}$

\end{document}

If you are only interested in changing the text fonts, but keeping the math fonts, instead of mathptmx you could use newtxtext package instead:

\documentclass[12pt,a4paper]{report}
\usepackage{newtxtext}

\begin{document}

$\mathcal{U}$

\end{document}

Answer 2

To obtain an ordinary \mathcal, please comment the

\usepackage{mathptmx}

line in your file.

BTW: do you really need all these packages?