%%%% prbla_11.ldf %%%% Created by Laurence D. Finston (LDF) Mon Nov 21 20:57:02 CET 2005 %% * (1) Copyright and License. %%%% This file is part of GNU 3DLDF, a package for three-dimensional drawing. %%%% Copyright (C) 2003, 2004, 2005, 2006, 2007, 2008, 2009, 2010, 2011, 2012, 2013, 2014, 2015, 2016, 2017, 2018, 2019, 2020, 2021, 2022, 2023 The Free Software Foundation, Inc. %%%% GNU 3DLDF is free software; you can redistribute it and/or modify %%%% it under the terms of the GNU General Public License as published by %%%% the Free Software Foundation; either version 3 of the License, or %%%% (at your option) any later version. %%%% GNU 3DLDF is distributed in the hope that it will be useful, %%%% but WITHOUT ANY WARRANTY; without even the implied warranty of %%%% MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the %%%% GNU General Public License for more details. %%%% You should have received a copy of the GNU General Public License %%%% along with GNU 3DLDF; if not, write to the Free Software %%%% Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA %%%% GNU 3DLDF is a GNU package. %%%% It is part of the GNU Project of the %%%% Free Software Foundation %%%% and is published under the GNU General Public License. %%%% See the website http://www.gnu.org %%%% for more information. %%%% GNU 3DLDF is available for downloading from %%%% http://www.gnu.org/software/3dldf/LDF.html. %%%% Please send bug reports to Laurence.Finston@gmx.de %%%% The mailing list help-3dldf@gnu.org is available for people to %%%% ask other users for help. %%%% The mailing list info-3dldf@gnu.org is for the maintainer of %%%% GNU 3DLDF to send announcements to users. %%%% To subscribe to these mailing lists, send an %%%% email with ``subscribe '' as the subject. %%%% The author can be contacted at: %%%% Laurence D. Finston %%%% c/o The Free Software Foundation, Inc. %%%% 51 Franklin St, Fifth Floor %%%% Boston, MA 02110-1301 %%%% USA %%%% Laurence.Finston@gmx.de %% Run these commands: %% 3dldf prbla_11.ldf %% mpost prbla_11 %% tex prbla_11.txt %% dvips -o prbla_11.ps prbla_11.dvi %% gv prbla_11.ps & %% *** (3) The intersection of a `parabola' and a `plane'. verbatim_metapost "verbatimtex \magnification=\magstep5 \font\large=cmr12 etex"; focus f; set f with_position (-5, 10, -20) with_direction (-5, 10, 100) with_distance 15; pickup pencircle scaled (1mm, 1mm); beginfig(1); parabola prb[]; set prb0 with_parameter 3 with_extent 12; set prb1 with_parameter 3 with_extent 30; draw prb1 dashed with_dots; draw prb0; rectangle r; r := unit_rectangle scaled (30, 0, 15) rotated (75, 20) shifted (5, 0, 3); draw r with_color red; plane pln; pln := get_plane r; bool_point_vector bpv; bpv := prb0 intersection_points pln; message "bpv:"; show bpv; point p[]; p0 := bpv0; p1 := bpv1; path pth[]; pth0 := p0 -- p1; bool_point_vector cpv; cpv := r intersection_points pth0; p2 := cpv0; p3 := cpv1; pth1 := p2 -- p3; draw pth1 dashed with_dots with_color red; %% **** (4) pickup pencircle scaled (1mm, 1mm); verbatim_metapost "pickup pencircle scaled .75mm"; if size bpv > 0: dotlabel.top("$p_0$", bpv0) with_dot_color blue; fi; if size bpv > 1: dotlabel.ulft("$p_1$", bpv1) with_dot_color blue; fi; if false: if size cpv > 0: dotlabel.urt(2, cpv0) with_dot_color blue; fi; if size cpv > 1: dotlabel.lft(3, cpv1) with_dot_color blue; fi; fi; %% **** (4) endfig with_focus f; verbatim_metapost "end"; end;