Cfrgtkky

I am trying to loop through a parameter to produce shifted graphs in grouppplots, as in the following MWE, however the value of k doesn't seem to be recognized in the argument of sin, i.e. the black lines are not shifted. I inserted a red line with shift 0.25 manually for comparison. What did I do wrong?

documentclass{standalone}



usepackage{pgfplots}

usepgfplotslibrary{groupplots}

begin{document}



begin{tikzpicture}

begin{groupplot}[group style={group size=1 by 3},width=textwidth,height=4cm,xmin=0,xmax=2,samples=200]

pgfplotsforeachungrouped k in {0,0.25,0.5}{

  nextgroupplot

  addplot[domain=0:2] gnuplot {sin(2*pi*(x - k))} node[above,pos=0.5]{k};

  addplot[domain=0:2,red,dashed] gnuplot {sin(2*pi*(x - 0.25))} node[above,pos=0.5]{k};

}

end{groupplot}

end{tikzpicture}



end{document}

Output:

Welcome to the expanding universe! (Yes, these expansion tricks can easily drive one close to madness. ;-))

documentclass{standalone}



usepackage{pgfplots}

usepgfplotslibrary{groupplots}

begin{document}



begin{tikzpicture}

begin{groupplot}[group style={group size=1 by 3},width=textwidth,height=4cm,xmin=0,xmax=2,samples=200]

pgfplotsinvokeforeach{0,0.25,0.5}{

  nextgroupplot

  edeftemp{noexpandaddplot[domain=0:2] gnuplot {sin(2*pi*(x - #1))}

  node[above,pos=0.5]{#1};}

  temp

  edeftemp{noexpandaddplot[domain=0:2,red,dashed] gnuplot {sin(2*pi*(x -

  0.25))} node[above,pos=0.5]{#1};}

  temp

}

end{groupplot}

end{tikzpicture}

end{document}

"EXPLANATION": When playing with pgfplots for a while, one comes across some standard tricks which one applies until one gets the desired result. ;-)