Postscript Parabola

%!PS

% author codework10101@gmail.com
% created on 06/12/2019


% Program draws a parabola (y = x^2) in the
% center of U.S.-Letter size (8.5 x 11 inch) paper.
% 1 inch is 72 points, that is the length of
% 1 inch is 72 smaller lengths called points



% definitions
/inch { 72 mul } def
/pt { 1 72 div mul } def % or /pt { 72 div } def
/cn { 255 div } def      % normalize color scale to be [0, 1]



% move scale from points to inches
1 inch 1 inch scale



% move origin to center of U.S.-Letter paper (4.25 inch, 5.5 inch)
4.25 5.5 translate



%=================================================
% PARABOLA: Y = X^2, (-0.98 inch < X < +0.98 inch)
%-------------------------------------------------
3 pt setlinewidth
/n 100 def
/dx 1 n div def  % 0.01 inches



% positive symmetry: 0 <= X < +0.98 inch
150 cn 206 cn 180 cn setrgbcolor
newpath
0 0 moveto
0 1 n 1 sub {
    dx mul
    %dup == %<-- to print values uncomment this
    dup dup mul lineto
} for
stroke



% negative symmetry: -0.98 inch < X < 0
255 cn 111 cn 105 cn setrgbcolor
newpath
0 0 moveto
1 1 n 1 sub {
    dx mul
    -1 mul
    %dup == %<-- to print values uncomment this
    dup dup mul lineto
} for
stroke



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