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Original Message (ID '390426') By yehuda:
As in theory, one should assign a value to the argument only after taking the derivative D[n[10],x] is the opposite of that The pattern n[10] is independent of the variable x, so the derivative is zero and when comparing 0 to 0 the result is True use n'[10] == 0 or Derivative[1][n][10] (which is the true code representing n'[10] so, your code should be eq = Gx + D[Dif*\!\( \*SubscriptBox[\(\[PartialD]\), \(x\)]\(n[x]\)\), x] - Kr (n[x] - n0) == 0; bcs = {n'[10] == 0, n[0] == n0}; Gx = 5; Dif = 2; Kr = 3; n0 = 1.5; NDSolve[{eq, bcs}, n[x], {x, 0, 10}] yehuda