#!/usr/bin/gnuplot

set terminal png
set output "diffeq.png"

set key off

set style line 1 lt 8
set style line 2 lt 2 lw 3
set style line 3 lt 1 lw 3

# set yzeroaxis lt -1

set parametric

plot [x=-10:10] [-10:10] [-25:25] \
x,0 ls 1, \
x,x+1 ls 1, \
x,-x+1 ls 1, \
x,2*x+4 ls 1, \
x,-2*x+4 ls 1, \
x,3*x+9 ls 1, \
x,-3*x+9 ls 1, \
x,4*x+16 ls 1, \
x,-4*x+16 ls 1, \
x,5*x+25 ls 1, \
x,-5*x+25 ls 1, \
x,6*x+36 ls 1, \
x,-6*x+36 ls 1, \
x,7*x+49 ls 1, \
x,-7*x+49 ls 1, \
x,8*x+64 ls 1, \
x,-8*x+64 ls 1, \
x,9*x+81 ls 1, \
x,-9*x+81 ls 1, \
x,10*x+100 ls 1, \
x,-10*x+100 ls 1, \
x,11*x+121 ls 1, \
x,-11*x+121 ls 1, \
x,-(.25)*(x*x) ls 2, \
(x-12),(x-12)+1 ls 3, \
(x+12),-(x+12)+1 ls 3, \
(x/5),-(.25)*((x/5)*(x/5)) ls 3

% MatLab code
h = figure
hold on
box on
x = [-10 10];
plot(x,[0 0]);
V = [1:1:11];
for i=1:numel(V)
 plot(x,V(i)*x+V(i)^2,'b',x,-V(i)*x+V(i)^2,'b');
end
x = [-10:0.1:10];
plot(x,-0.25*x.*x,'g','LineWidth',3);
plot(x-12, (x-12)+1,'r','LineWidth',2);
plot(x+12,-(x+12)+1,'r','LineWidth',2);
plot((x/5),-.01*x.*x,'r','LineWidth',2);
axis([-10 10 -25 25]);
axis square

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