How do I use the sin function in LaTeX3

Question

I am exploring some of the LaTeX3 routines and syntax. How do I get to use functions such as sin etc. I get an error with the sin function in the following (please uncomment sin function to view the error) :

\documentclass{article}
\usepackage{expl3}

\begin{document}

\ExplSyntaxOn
\newcommand*\sampleCalculation{%
  \fp_new:N  \mynumber
  \fp_set:Nn \mynumber{150}
  \fp_sub:Nn \mynumber{5}
  \fp_add:Nn \mynumber{-1}
  \fp_div:Nn \mynumber{12}
  \fp_mul:Nn \mynumber{0.0001}
  \fp_sub:Nn \mynumber{-38}
  \fp_abs:N  \mynumber
  \fp_neg:N  \mynumber
 %\fp_sin:N  \mynumber
  \fp_use:N  \mynumber 
 }

% aliases 
\let\real\fp_new:N
\let\realset\fp_set:Nn
\let\realadd\fp_add:Nn
\let\realsub\fp_sub:Nn
\let\realdiv\fp_div:Nn
\let\realmul\fp_mul:Nn



\newcommand\sampleCalculations{%
  \real    \Z
  \realset \Z{150}
  \realsub \Z{5}
  \realadd \Z{-1}
  \realdiv \Z{12}
  \realmul \Z{0.0001}
  \Z
}

\ExplSyntaxOff

\sampleCalculation

\sampleCalculations


\end{document}

Answer 1

The FPU for LaTeX3 has undergone some major changes. Up to the version included in the DVD of TeX Live 2012 (mid-June 2012) the 'old' FPU worked one way. The improved FPU, available from the development repository and scheduled for release to CTAN some time in late June 2012, is expandable and features a number of improvements.

Updated (expandable) FPU answer

Most assignments should be done using \fp_set:Nn or \fp_gset:Nn. The second argument of those macros accepts arbitrary floating point expressions.

\fp_set:Nn \l_my_fp { sin ( 7.415e-1 + 2.4 ) }

Original (non-expandable) FPU answer

Currently, \fp_sin:Nn needs two arguments, the variable in which the result is stored and the angle (in radians):

\fp_sin:Nn \l_my_fp { 3.1415 }

The best syntax for fp operations is something that feedback would be very welcome on. The current thinking is that working out a sine makes more sense with separate input and output arguments than a hypothetical

\fp_set:Nn \l_my_fp { 3.1415 }
\fp_sin:N \l_my_fp

This is not set in stone: the fp module is much more recent than a lot of the rest of expl3 and thus needs a good work-out. This syntax question is one such area. Another is using degrees or radians. The calculation is in radians internally, so perhaps \fp_rad_to_deg:N and \fp_deg_to_rad:N might be a useful compromise approach.

I'd also point out that there are currently no arc functions: there was a need for sine and cosine for other purposes, so I got these done. I'll do the arc functions when the demand arises.