function y=f1(x,t)

%% State variable derivatives for solar car simulation
%% suitable for use in lsode()
%% x(1)  is velocity,     x(2)  is position
%% x'(1) is acceleration, x'(2) is velocity
%% See race.m for more info.

global pf delv
if (length(x) != 2)
   error("what")
end

k=floor(x(1)/delv)+1;
if (k<1 || k>size(pf,1))
   error("out of bounds")
end
y=[ polyval(pf(k,:),x(1)), x(1) ];