[Tex/LaTex] Reduce vertical space between chapter name and multi-line chapter title

chaptersspacing

I am trying to make my thesis satisfy my grad school's requirement. The titles of my chapters are long. What they suggest and I quote is
"Entire chapter titles must be single spaced. For example, on page 6 the line Between “Chapter 2” and “A loooooooong” should have the same single line spacing as between the lines “A loooooooong” and “multi-line title that I have”."

I have tried titlesec. But it keeps putting "nin]0.0.0.0.0.0 5.87494pt" on my first page. So it would be great if this problem can be fixed in some other way.

Here is my MWE

    \documentclass[12pt]{report}
    \usepackage{amsmath,amsthm,amssymb,latexsym,amscd}
    \usepackage{setspace}
    \usepackage{titlesec}

    \begin{document}

    \chapter{A loooooooooooooooong multi-lines title that I have}

    \end{document}

Best Answer

report class uses the macro \@makechapterhead to set chapter heads, so you can just copy its definition and comment out the space:

enter image description here

 \documentclass[12pt]{report}
    \usepackage{amsmath,amsthm,amssymb,latexsym,amscd}
    \usepackage{setspace}
   \makeatletter
\def\@makechapterhead#1{%
  \vspace*{50\p@}%
  {\parindent \z@ \raggedright \normalfont
    \ifnum \c@secnumdepth >\m@ne
        \huge\bfseries \@chapapp\space \thechapter
        \par\nobreak
%        \vskip 20\p@
    \fi
    \interlinepenalty\@M
    \Huge \bfseries #1\par\nobreak
    \vskip 40\p@
  }}

   \makeatother

    \begin{document}

    \chapter{A loooooooooooooooong multi-lines title that I have}

    \end{document}
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