Why there is a single output for the value c?

Recently I would like to plot a figure about concentration with respect to time, but not similar to exercises before I did, in the figure only a straight line can be obtained and one c value, instead of a matrix of c value, can be got. So I am confused what happened with my coding? Could anyone recognize and point out for me? Thank you so much! The coding is shown as follows:

function c = AS_BTC(t)
  t = 0:100:36000;
  Daq = 1e-9;
  v = 9.37e-6;
  aL = 6.7e-3;
  C0 = 20;
  n = 0.32;
  Cbg = 0;
  Dl = Daq * n + aL * v;
  x = 0.25;
  c = Cbg + (C0 - Cbg)/2 * erfc((x - v * t)/(2 * sqrt(Dl * t)));
  plot(t,c);
 end

Answer 1

[Walter Roberson]

   c = Cbg + (C0 - Cbg)/2 * erfc((x - v * t) ./ (2 * sqrt(Dl * t)));