set term pdf
set output 'quad-sext-field.pdf'
unset border
unset xtics
unset ytics
f(x) = a*x**2
a=-30
g(x) = b*x 
b=200
set xrange [-5:5]
set zeroaxis dt "-" lt 2
plot f(x) not, g(x) not
print 'quad-sext-field.pdf'