# A strange partial symbol into newtx package

Considering that in these weeks the newtx package is changing versions continuously from my old question Modify characters of mt2pro[lite] using Times, using this MWE,

\documentclass[a4paper,12pt]{article}
\usepackage{newtxtext,newtxmath}
%%%%%%%%%%%%%%%%%%%%%% Nuovo \partial
\DeclareFontFamily{U}{nxlmi}{}
\DeclareFontSubstitution{U}{nxlmi}{m}{it}
\DeclareFontShape{U}{nxlmi}{m}{it}{
<-6.3>    nxlmi05
<6.3-8.6> nxlmi07
<8.6->    nxlmi0
}{}
\DeclareFontShape{U}{nxlmi}{b}{it}{
<-6.3>    nxlbmi05
<6.3-8.6> nxlbmi07
<8.6->    nxlbmi0
}{}
\renewcommand{\partial}{{\text{\usefont{U}{nxlmi}{m}{it}\symbol{64}}\mspace{1mu}}}

\begin{document}
$\frac{\partial x}{\partial t}, \frac{\partial \overline{E}}{\partial t}$
\end{document}

I obtained these \partial symbol (number 64 of newtx package).

But compiling with TeXWorks (with last update of MikTeX) I have obtained another symbol, as from image,

The font is pretty but it is small compared to the size of the lowercase and uppercase of each characther. Now also if I remove the command \renewcommand{\partial}{{\text{\usefont{U}{nxlmi}{m}{it}\symbol{64}}\mspace{1mu}}} I will have the \partial symbol of mtpro2 lite.

I have not obtain the \partial symbol that exist into the guide of newtx. Why and what is the strategy to get the partial symbol of the first image?

As suggested by the very good author of newtx Michael Sharpe that I thank so much, the font nxlmi and its variants contain symbols from Libertine, and are called when I supply the libertine option to newtxmath. It is ntxmi and variants that contain the symbols appropriate to newtxtext. Therefore I have changed my original code,

\documentclass{article}
\usepackage[lite]{mtpro2}
\usepackage{newtxtext}
\DeclareFontFamily{U}{ntxmi}{}
\DeclareFontSubstitution{U}{ntxmi}{m}{it}
\DeclareFontShape{U}{ntxmi}{m}{it}{
<-6.3>    nxlmi05
<6.3-8.6> nxlmi07
<8.6->    nxlmi0
}{}
\DeclareFontShape{U}{ntxmi}{b}{it}{
<-6.3>    ntxbmi05
<6.3-8.6> ntxbmi07
<8.6->    ntxbmi0
}{}
\renewcommand{\partial}{{\text{\usefont{U}{ntxmi}{m}{it}\symbol{64}}\mspace{1mu}}}

\begin{document}
$\partial t$
\end{document}

But with the new code I get the following error message:

! Undefined control sequence.
\partial ->{\text
{\usefont {U}{ntxmi}{m}{it}\symbol {64}}\mspace {1mu}}
l.23 \partial
t
?

If I remove the new definition of \partial -- \renewcommand{\partial}{{\text{\usefont{U}{ntxmi}{m}{it}\symbol{64}}\mspace{1mu}}} -- I get default \partial symbol of the package mtpro2.

\documentclass{article}
\usepackage[lite]{mtpro2}
\usepackage{newtxtext}

\DeclareFontFamily{U}{ntxmi}{}
\DeclareFontSubstitution{U}{ntxmi}{m}{it}
\DeclareFontShape{U}{ntxmi}{m}{it}{
<-6.3>    nxlmi05
<6.3-8.6> nxlmi07
<8.6->    nxlmi0
}{}
\DeclareFontShape{U}{ntxmi}{b}{it}{
<-6.3>    ntxbmi05
<6.3-8.6> ntxbmi07
<8.6->    ntxbmi0
}{}

\begin{document}
$\partial t$
\end{document}

How can I solve the problem? I am waiting patiently for an possible answer.

• Apparently, the character has changed in the last version of newtxmath. Just remove the redefinition of \partial. – egreg Oct 21 '19 at 13:59
• The error message shows up because of the unrecognized \text command. Load the amsmath package to get rid of the error message. – Mico Nov 1 '19 at 21:46
• @Mico Addendum: On my structure.tex for my book I have loaded mathtools instead of amsmath but I have always the new symbol :-(. Thank you very much. – Sebastiano Nov 1 '19 at 21:50
• @Sebastiano - The mathtools package loads the amsmath package automatically. :-) – Mico Nov 1 '19 at 21:51
• @Sebastiano - Please see the answer I just posted. To me, there's a significant visual distinction between the two \partial styles. – Mico Nov 1 '19 at 22:28

(too long for a comment, hence posted as an answer)

There have several updates to the newtxmath package in recent days. In what follows below, I use the version that's current as of today, i.e., 1 November 2019.

First off, here's what I get when I load the mtpro2 package and run $\partial\ \scriptstyle\partial\ \scriptscriptstyle\partial$ in the body of the document:

Next, here's what I get when I load the newtxmath package. The upper row is without the \renewcommand instruction, while the lower row is with the redefinition of \partial. To me, there's not a huge, but still an easy-to-spot visual difference.

\documentclass{article}
%\usepackage[lite]{mtpro2}
\usepackage{amsmath} % for "\text" macro
\usepackage{newtxtext,newtxmath}
\DeclareFontFamily{U}{ntxmi}{}
\DeclareFontSubstitution{U}{ntxmi}{m}{it}
\DeclareFontShape{U}{ntxmi}{m}{it}{
<-6.3>    nxlmi05
<6.3-8.6> nxlmi07
<8.6->    nxlmi0
}{}
\DeclareFontShape{U}{ntxmi}{b}{it}{
<-6.3>    ntxbmi05
<6.3-8.6> ntxbmi07
<8.6->    ntxbmi0
}{}

\begin{document}
$\partial\ \scriptstyle\partial\ \scriptscriptstyle\partial$

\renewcommand{\partial}{\text{\usefont{U}{ntxmi}{m}{it}\symbol{64}}\mspace{1mu}}

$\partial\ \scriptstyle\partial\ \scriptscriptstyle\partial$
\end{document}
• Most kind Mico but isn't there another family of fonts as ntxmi into DeclareFontFamily.... that provides a better new \partial than newtx? – Sebastiano Nov 1 '19 at 22:43
• @Sebastiano - I'm afraid I've kind of lost track of your objectives. Which math font package(s) do you employ, and which style of \partial are you trying to achieve? If you're using newtxmath and if you want a more "upright" partial symbol, give \uppartial a try. – Mico Nov 1 '19 at 22:46
• As you well know I use newtxtext with mtpro2 (no newtxmath) and do not change these packages :-). Don't worry you've done the maximum of the maximum. Thank you always for everything from the heart. – Sebastiano Nov 1 '19 at 22:52