set term wxt 1
unset arrow
set   arrow 1 from -1,0 to -1,2.5      nohead
set   arrow 2 from -1,0 to  0,0        nohead
set   arrow 3 from  0,0 to  0,1        nohead
set   arrow 4 from  0,1 to  1,1        nohead
set   arrow 5 from  1,1 to  1,2.5      nohead

system "gfortran -O2 boxgrav.f90 -o b"
plot [-1.1:1.1][-0.1:2.5] "< echo -0.5 2 1 0 3.5 0.001|./b;cat box.dat" u 2:3 w l not
system "tail -n 1 box.dat"
