Odtnhj

I would like to define a variable j in a loop foreach i in 2, 4, 6 and use j to labels of the nodes.

Here is my code:

documentclassstandalone
usepackagebalance,complexity,pgfplots,tikz,tikz-3dplot
usetikzlibrarycalc

begindocument


begintikzpicture[scale=0.4]

 def half 0.5;

 foreach i in 2, 4, 6
 
 def j i*half;
 node[draw=none] at (i,0) $X_j$;
 node[draw=none] at (-i,0) $X'_j$;
 


endtikzpicture
enddocument

I would like to get this output:

Instead, I get this:

How can I use mathematical operators to modify the label of a node?

Use the pgfmath macros (pgfmathsetmacro for float calculations and pgfmathtruncatemacro if you only want the integer part).

documentclassstandalone
usepackagetikz

begindocument


begintikzpicture[scale=0.4]
 pgfmathsetmacrohalf 0.5;
 foreach i in 2, 4, 6
 
 pgfmathtruncatemacroji*half;
 node[draw=none] at (i,0) $X_j$;
 node[draw=none] at (-i,0) $X'_j$;
 
endtikzpicture
enddocument

You can do the calculations within the foreach loop with

foreach i [evaluate=i as moitie using int(i/2)] in 2, 4, 6 

see page 904 of manual 3.0.1a.

documentclassstandalone
usepackagetikz

begindocument
begintikzpicture[scale=0.4]
foreach i [evaluate=i as moitie using int(i/2)] in 2, 4, 6
 
 node[draw=none] at (i,0) $X_moitie$;
 node[draw=none] at (-i,0) $X'_moitie$;
 
endtikzpicture
enddocument