latin-modernsans-serifsmall-caps
How can I have the sans serif small caps with this fonts?
\documentclass{book}
% Latin Modern with oldstyle digits
\usepackage[%
rm={oldstyle,proportional},%
sf={oldstyle,proportional},%
tt={oldstyle=false,proportional=false,monowidth}%
]{cfr-lm}
\begin{document}
\sffamily\scshape test
\end{document}
If I understand your question correctly, you are trying to get a document typeset using a sans-serif font rather than the "ordinary" serif font. In addition, you want the font that's used in math to be upright rather than "slanted". The only math font I'm familiar with that's upright rather than slanted is the so-called "Euler" font; it goes reasonably well with Computer Modern fonts, both serif and sans-serif. If the Euler font suits your needs, you should add the following commands to the preamble of your document:
\renewcommand{\encodingdefault}{T1}
\usepackage[T1]{fontenc}
\renewcommand{\familydefault}{\sfdefault}
\usepackage{eulervm}
It is a big difference. It depends on the tastes of Jörg Knappen who designed the European Modern fonts and apparently liked less heavy sans serif fonts.
With \usepackage{lmodern} you'll get the same weight.
Best Answer
There is no small caps shape in the Latin Modern Sans typeface family (either in Type1 or in OpenType format).
So the answer is "no, you can't have sans serif small caps", because the shape doesn't exist.
See this paper by W. Robertson for a description of the available faces and shapes.