Cfrgtkky

On the bottom you will find a minimal example of my code (perhaps a little bit too much packages).

My problem is that I would like to have a very small separation between each column. That's why I inserted a column with width 0.01cm, but somehow these columns are way larger.

Did I make a mistake with my definition or is there an easier way?

documentclass[letter,11pt,twoside]{article}

usepackage{tikz}    usepackage{amsmath}    usepackage{breqn}

usepackage{stmaryrd}    usepackage{pdfpages}    usepackage{pstricks}

usepackage{pst-plot}    usepackage{pst-pdf}    usepackage{multirow}

usepackage{subfig,rotating,longtable,lscape,geometry,layouts}

usepackage{rotating,tabularx}    usepackage{verbatim} usepackage{placeins}

usepackage{listings}    usepackage{float,mdwlist,enumerate}    usepackage{etex}

usepackage{makecell}    usepackage{float,mdwlist,enumitem}    usepackage{siunitx}    usepackage{dcolumn}



newcolumntype{d}[1]{D{.}{.}{#1}}

newcommand{muc}[2]{multicolumn{1}{C{#1}}{#2}}

newcommand{mucThree}[2]{multicolumn{3}{C{#1}}{#2}}



newcolumntype{P}[1]{>{centeringarraybackslash}p{dimexpr#1textwidth-2tabcolseprelax}}



newcolumntype{C}[1]{>{centeringarraybackslash}p{#1}} 



begin{document}  



begin{table}[h!]    

    caption{Bereits erbrachte Leistungen}   

    begin{tabular}{C{1.5cm}|p{0.01cm}|C{1.5cm}C{0.01cm}C{1.5cm}C{0.01cm}C{1.5cm}C{0.01cm}C{1.5cm}C{0.01cm}C{1.5cm}C{0.01cm}C{1.5cm}C{0.01cm}C{1.5cm}C{0.01cm}C{1.5cm}C{0.01cm}C{1.5cm}C{0.01cm}} 

&&&mucThree{3cm}{$c_{S_1}=18$} && mucThree{3cm}{$c_{S_1}=20$} &&mucThree{3cm}{$c_{S_1}=22$} \ cline{3-7} cline{9-13}           

&& $Eleft[pi_R^{bar{c}}right]$ && $Eleft[pi_R^{c}right]$ && $Eleft[pi_R^{c}right]/Eleft[pi_R^{bar{c}}right]$ 

&& $Eleft[pi_R^{bar{c}}right]$ && $Eleft[pi_R^{c}right]$ && $Eleft[pi_R^{c}right]/Eleft[pi_R^{bar{c}}right]$ &&$Eleft[pi_R^{bar{c}}right]$ && $Eleft[pi_R^{c}right]$ && $Eleft[pi_R^{c}right]/Eleft[pi_R^{bar{c}}right]$ \

$c_{S_2}=18$    &&  4208    &&  4364    &&  1,04    &&  3934    &&  4236    &&  1,08    &&  3819    &&  4109    &&  1,08 

    end{tabular}

end{table}

end{document}

Definitely too many packages for the example. Note also that

1. 
   mdwlist has been unmaintained for more than 20 years


2. loading both enumitem and enumerate is wrong


3. 
   pstricks and tikz? Are you sure?


4. 
   letter is not an option for article; it should be letterpaper (or omitted, as it's the default)

Now the table: most of the space is eaten up by the headers; since they're repeated, it's better to give them a name and repeat that, with an explanation at the bottom.

I recommend using siunitx features and booktabs.

documentclass{article}



usepackage{array,siunitx,booktabs}



begin{document}  



begin{table}[h!]    

caption{Bereits erbrachte Leistungen}   



begin{tabular*}{textwidth}{

  @{extracolsep{fill}}

  l

  *{3}{

    S[table-format=4.0]

    S[table-format=4.0]

    S[table-format=1.2]

  }

  @{}

}

toprule

& multicolumn{3}{c}{$c_{S_1}=18$}

& multicolumn{3}{c}{$c_{S_1}=20$}

& multicolumn{3}{c}{$c_{S_1}=22$} \

cmidrule(lr){2-4} cmidrule(lr){5-7} cmidrule(l){8-10}

& {(1)} & {(2)} & {(3)}

& {(1)} & {(2)} & {(3)}

& {(1)} & {(2)} & {(3)} \

midrule

$c_{S_2}=18$

& 4208 & 4364 & 1,04 & 3934 & 4236 & 1,08 & 3819 & 4109 & 1,08 \

$c_{S_2}=18$

& 4208 & 4364 & 1,04 & 3934 & 4236 & 1,08 & 3819 & 4109 & 1,08 \

$c_{S_2}=18$

& 4208 & 4364 & 1,04 & 3934 & 4236 & 1,08 & 3819 & 4109 & 1,08 \

$c_{S_2}=18$

& 4208 & 4364 & 1,04 & 3934 & 4236 & 1,08 & 3819 & 4109 & 1,08 \

$c_{S_2}=18$

& 4208 & 4364 & 1,04 & 3934 & 4236 & 1,08 & 3819 & 4109 & 1,08 \

midrule[heavyrulewidth]

multicolumn{10}{@{}l@{}}{%

  (1): $E[pi_R^{bar{c}}]$;qquad

  (2): $E[pi_R^{c}]$;qquad

  (3): $E[pi_R^{c}]/E[pi_R^{bar{c}}]$%

}

end{tabular*}

end{table}

end{document}