pendulum.deq

defequ

unknown[0]:="x";
unknown[1]:="v";
x'(t):={ v };
v'(t):={ -x-k*v };
x_:=1;v_:=1;
  t0:=0;
maxt:=30;
  dt:=0.04;
E(t):={ x*x+v*v };
k:=0.2;
c:=2;