Load integral sign from eulervm

Question

I want to write a book for university and I want to have the "german" integral symbol in it. I tried using mathabx and wasysym but I don't like them. But I like the integral symbol in eulervm.
How do I load this symbol?

I have already tried:

\documentclass{article}
\let\int\undefined
\DeclareSymbolFont{largesymbols}{OMX}{eulervm}{m}{n}
\DeclareMathSymbol{\int}{\mathop}{largesymbols}{"52}
\begin{document}
\[ \int \]
\end{document}

But that just loads the normal "american" integral symbol.

What am I doing wrong?

Answer 1

If you redefine the largesymbols font, all large operators will be taken from the Euler font. Moreover, the call is wrong:

\DeclareSymbolFont{eulargesymbols}{U}{zeuex}{m}{n}
\DeclareMathSymbol{\intop}{\mathop}{eulargesymbols}{"52}

Here is the picture (on the right the usual symbol)

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How does one discover what should be done? Well, it depends on the font one has to use. Let's make an example: we want some large symbols from the font used by mathpazo.

We find in mathpazo.sty what font is used:

\DeclareSymbolFont{largesymbols}{OMX}{zplm}{m}{n}

Thus we just change the symbolic name to something like pazolargesymbols and do as the previous case; since the encoding is OMX, which is the same normally used for math extension fonts, we know that the integral will be in the same slot as in the usual setting:

\DeclareMathSymbol{\intop}{\mathop}{pazolargesymbols}{"52}

One can find the standard definition in fontmath.ltx.

If the encoding is non standard, as in the case of eulervm, we need to check for the slot. However, eulervm.sty doesn't redefine \intop, so we can be confident that the usual slot is good. It could be different for other symbols.

Note that we have to define \intop rather than \int, because the latter is defined by LaTeX as

\def\int{\intop\nolimits}

The amsmath package does a different definition of \int, but it uses \intop for the symbol as well.