I'm drawing a diagram for a physical phenomenon, "motion in one dimension". I have this figure with a tikzpicture:




      \draw[help lines] (0,0) grid (8,2);
      \draw[thick] (0,0) -- (8,0);
      \node [right] at (8.25,0) {x (m)};
      \node [below] at (0,0) {-40};
      \node [below] at (1,0) {-30};
      \node [below] at (2,0) {-20};
      \node [below] at (3,0) {-10};
      \node [below] at (4,0) {0};
      \node [below] at (5,0) {10};
      \node [below] at (6,0) {20};
      \node [below] at (7,0) {30};
      \node [below] at (8,0) {40};
      \draw [draw=black, fill=particle, opacity=0.5]
         (1,0) rectangle (2,1);
      \draw [draw=black, fill=particle]
         (6,0) rectangle (7,1);
   \caption{Motion in one dimension} \label{fig:tbh1}


Compiling with pdflatex, I get this error:

! Package pgfkeys Error: The key '/tikz/opacity' requires a value. I am going to ignore this key.

... on this line:

l.73 ...w [draw=black, fill=particle, opacity=0.5]

Didn't I specify a value for the opacity already? Why am I getting this error?

EDIT: Edited the code to be compilable.

  • 3
    Welcome to TeX.SX! Please make your code compilable (if possible), or at least complete it with \documentclass{...}, the required \usepackage's, \begin{document}, and \end{document}. That may seem tedious to you, but think of the extra work it represents for TeX.SX users willing to give you a hand. Help them help you: remove that one hurdle between you and a solution to your problem.
    – jub0bs
    Aug 10, 2014 at 18:32
  • 1
    I don't get an error with your code! It works as it should
    – cgnieder
    Aug 10, 2014 at 18:40
  • 1
    @Jubobs: Thanks for the warm welcoming! I've edited the code to be compilable. Aug 10, 2014 at 18:40
  • 1
    Hi welcome indeed. There shouldn't be a problem with the given code. Do you have another setting that is named particle somewhere?
    – percusse
    Aug 10, 2014 at 18:41
  • 2
    Not relevant to the issue, but your x-axis labels should be in math mode, particularly as you've otherwise got - appearing as a hyphen not a minus sign.
    – Joseph Wright
    Aug 10, 2014 at 18:55

1 Answer 1


Further investigation of the error led to the fact that when the line


was omitted from the preamble, the code compiled just fine. (I didn't put this line into the code in the question, because, I thought it was irrelevant. Another lesson learned.)

To fix the issue, I added the line


to the preamble. It didn't work at first, but when I upgraded PGF/TikZ from 2.10 to 3.00, it did.

  • Do you kind explaining us how to update PGF/TikZ?
    – bkarpuz
    Sep 1, 2017 at 13:10

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