Hello!
 
This is my first thread here.
 
I typed the stiffness matrix of a beam in its local coordinates. My code:
 
\startpmatrix
    %----------------------------------------------- 1
    \NC \cfrac{SE}{L}
    \NC 0
    \NC 0
    \NC 0
    \NC 0
    \NC 0
    \VL
    \NC -\cfrac{SE}{L}
    \NC 0
    \NC 0
    \NC 0
    \NC 0
    \NC 0
    \NR
    %----------------------------------------------- 2
    \NC 0
    \NC \cfrac{12EI_z}{L^3}
    \NC 0
    \NC 0
    \NC 0
    \NC \cfrac{6EI_z}{L^2}
    \VL
    \NC 0
    \NC -\cfrac{12EI_z}{L^3}
    \NC 0
    \NC 0
    \NC 0
    \NC \cfrac{6EI_z}{L^2}
    \NR
    %----------------------------------------------- 3
    \NC 0
    \NC 0
    \NC \cfrac{12EI_y}{L^3}
    \NC 0
    \NC -\cfrac{6EI_y}{L^2}
    \NC 0
    \VL
    \NC 0
    \NC 0
    \NC \cfrac{12EI_y}{L^3}
    \NC 0
    \NC -\cfrac{6EI_y}{L^2}
    \NC 0
    \NR
    %----------------------------------------------- 4
    \NC 0
    \NC 0
    \NC 0
    \NC \cfrac{GJ}{L}
    \NC 0
    \NC 0
    \VL
    \NC 0
    \NC 0
    \NC 0
    \NC \cfrac{GJ}{L}
    \NC 0
    \NC 0
    \NR
    %----------------------------------------------- 5
    \NC 0
    \NC 0
    \NC -\cfrac{6EI_y}{L^2}
    \NC 0
    \NC \cfrac{4EI_y}{L}
    \NC 0
    \VL
    \NC 0
    \NC 0
    \NC \cfrac{6EI_y}{L^2}
    \NC 0
    \NC \cfrac{4EI_y}{L}
    \NC 0
    \NR
    %----------------------------------------------- 6
    \NC 0
    \NC \cfrac{6EI_z}{L^2}
    \NC 0
    \NC 0
    \NC 0
    \NC \cfrac{4EI_z}{L}
    \VL
    \NC 0
    \NC -\cfrac{6EI_z}{L^2}
    \NC 0
    \NC 0
    \NC 0
    \NC \cfrac{4EI_z}{L}
    \NR
    \HL
    %----------------------------------------------- 7
    \NC -\cfrac{SE}{L}
    \NC 0
    \NC 0
    \NC 0
    \NC 0
    \NC 0
    \VL
    \NC \cfrac{SE}{L}
    \NC 0
    \NC 0
    \NC 0
    \NC 0
    \NC 0
    \NR
    %----------------------------------------------- 8
    \NC 0
    \NC -\cfrac{12EI_z}{L^3}
    \NC 0
    \NC 0
    \NC 0
    \NC -\cfrac{6EI_z}{L^2}
    \VL
    \NC 0
    \NC \cfrac{12EI_z}{L^3}
    \NC 0
    \NC 0
    \NC 0
    \NC -\cfrac{6EI_z}{L^2}
    \NR
    %----------------------------------------------- 9
    \NC 0
    \NC 0
    \NC \cfrac{12EI_y}{L^3}
    \NC 0
    \NC \cfrac{6EI_y}{L^2}
    \NC 0
    \VL
    \NC 0
    \NC 0
    \NC \cfrac{12EI_y}{L^3}
    \NC 0
    \NC -\cfrac{6EI_y}{L^2}
    \NC 0
    \NR
    %----------------------------------------------- 10
    \NC 0
    \NC 0
    \NC 0
    \NC \cfrac{GJ}{L}
    \NC 0
    \NC 0
    \VL
    \NC 0
    \NC 0
    \NC 0
    \NC \cfrac{GJ}{L}
    \NC 0
    \NC 0
    \NR
    %----------------------------------------------- 11
    \NC 0
    \NC 0
    \NC \cfrac{6EI_y}{L^2}
    \NC 0
    \NC \cfrac{4EI_y}{L}
    \NC 0
    \VL
    \NC 0
    \NC 0
    \NC \cfrac{6EI_y}{L^2}
    \NC 0
    \NC \cfrac{4EI_y}{L}
    \NC 0
    \NR
    %----------------------------------------------- 12
    \NC 0
    \NC -\cfrac{6EI_z}{L^2}
    \NC 0
    \NC 0
    \NC 0
    \NC \cfrac{4EI_z}{L}
    \VL
    \NC 0
    \NC -\cfrac{6EI_z}{L^2}
    \NC 0
    \NC 0
    \NC 0
    \NC \cfrac{4EI_z}{L}
    \NR
    %-----------------------------------------------
\stoppmatrix
 
After compiling my code I see that my matrix is a little ugly.
 
https://habrastorage.org/webt/la/qj/1c/laqj1cud6wjae6diwrvdwfpvfks.png
 
1. Vertical line is not a single line, but multiple small vertical lines.
I see little gaps between these small vertical lines.
 
2. I see text is too close to vertical and horizontal lines. I'd like
to set margins around vertical and horizontal lines but I didn't find
how to do this. I'm not sure if it's possible.
 
Please help me to make my matrix more beautiful.