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I would like to compute coords X and Y to build a figure :


\usepackage{tikz} % pour dessins
\usetikzlibrary{shapes, calc, arrows} % pour complement tikz



\coordinate (P1) at (\tan(\angleg)*\focale,1.5cm);
\end{tikzpicture}%<<<== must use well balanced curly-braces


but i have got an error :

Missing \endcsname inserted \coordinate (P1) at (\tan(32)

I tried to include the compute within $ but :

Paragraph ended before \tikz@cc@parse@factor was complete
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You just need braces, otherwise Tikz cannot recognize a calculation from a point ({tan(\angleg)*\focale},1.5cm). –  zeroth Jul 11 '13 at 13:32
many thanks and sorry...i have scanned some introductions notes to tikz, but i should have read in details... –  Patrick Dezecache Jul 11 '13 at 13:41
Many thanks for all participations ! I think i will use answers linked to tikz, but pstricks seems to be quite interessant too. great tools ! and a great teams to support it ! - patrick –  Patrick Dezecache Jul 11 '13 at 17:27

3 Answers 3

up vote 2 down vote accepted

Short answer is: Yes, you can.

Your error is that you're typing the function with a backslash \ which is the way to indicate to LaTeX that it's a command in the compilation. When calculating a number, functions shouldn't have a backslash, just tan(angleg) and so on.

For more complicated functions, use the curly bracket to indicate they are supposed to be together (as stated by @zeroth )({tan(\angleg)*\focale},1.5cm).

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I disagree with the one statement of the reply about the \ (backslash) :

  • the \tan must be replaced by 'tan' because you want the mathematical function to be aplied to the \angleg and not to write 'tan(58)'
  • you must keep the '\angleg' because TeX has no idea about 'angleg ' (it's pure text)

I agree with the reply about the {} (curly brackets), which are mandatory each time you have some () in the point definition.

But the full answer would be to use the $ syntax to compute the point coordinates :

\coordinate (P1) at ($({tan(\angleg)*\focale},1.5cm)$);

Futhermore, it could be better practice to replace

\def\gnat{<some math expresion>}


\pfgmathsetmacro{\gnat}{<some math expresion>}

because the calculation is then parsed and performed immediatly when using the latter.

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You're right about the backslash in \angleg, but it's not necessary to use the $ syntax from the calc library if you're only evaluating a mathematical expression in a coordinate component. The calc library is only necessary when you're performing calculations that use full coordinates. –  Jake Jul 11 '13 at 14:12

With PSTricks. Just for comparison purposes.

PSTricks equivalent for TikZ ({tan(\complement)*\radius},1.5) is

  • (+{Tan(\complement)*\radius},1.5)
  • (**{Tan(\complement)*\radius} 1.5)


%\pnode(**{Tan(\complement)*\radius} 1.5){P1}

enter image description here


In PSTricks, there are some ways to define a coordinate. It can be expressed in terms of existing nodes or mathematics expressions. With mathematics expression, we have 4 methods as follows.

  • RPN for both abscissa and ordinate.

    For example: (!2 3 mul 1 sub 2 0 add) is a point (5,2).

  • RPN for abscissa and algebraic for ordinate. The ordinate can be a function of x.

    For example: (*{2 3 add} {x-3}) is a point (5,2).

  • Algebraic for abscissa and RPN for ordinate. The abscissa can be a function of y.

    For example: (**{y*3-1} {1 1 add}) is a point (5,2).

  • Algebraic for both abscissa and ordinate.

    For example: (+{3+2},1+1) is a point (5,2).

The following example uses \def to express algebraic expression as a function of x, y or a constant.


    \pscircle*[linecolor=red](+{\f[2],\f[1]}){2pt}% its center is (3,1)
    \pscircle*[linecolor=green](*{1 0 add} {\f[x]}){2pt}% its center is (1,1)
    \pscircle*[linecolor=blue](**{\f[y]} {2 0 add}){2pt}% its center is (3,2)
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What's the difference between the + syntax and the ** syntax (apart from the fact that one needs a comma between the components, and the other doesn't)? –  Jake Jul 11 '13 at 14:56
@Jake: I will update my answer to accommodate more general cases. –  stalking is prohibited Jul 11 '13 at 14:57

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