enter image description here Why is the error coming and what should I do to resolve it enter image description here The code is


Plot[ Evaluate[y[r]/ sol1],{r,.000000001,.000001}]
  • $\begingroup$ Note that sol1 and sol are 2 different variables. $\endgroup$ Oct 26, 2020 at 19:41
  • $\begingroup$ @DanielHuber i changed it but now this is coming $\endgroup$
    – zeeman
    Oct 26, 2020 at 19:59
  • $\begingroup$ when i used Plot[ Evaluate[y[r]/. sol1],{r,.000000001,.000001}] still error was coming $\endgroup$
    – zeeman
    Oct 26, 2020 at 19:59
  • 1
    $\begingroup$ Please edit your question and add the code as text, not an image, so others can copy/paste and reproduce the problem. $\endgroup$ Oct 26, 2020 at 20:15
  • $\begingroup$ Use DSolveValue instead so you don't have to muck around with replacement rules. $\endgroup$ Oct 26, 2020 at 20:36

2 Answers 2


Your code contains: ry''[r]. You need a space between r and y.

But this does not solve your problem. DSolve seems not able to solve this. Maybe there is no closed form solution.

Trying to use NDSolve indicates that the system is unstable. The reason is that y'[30] is too far out, y'[10] will work.

sol = y /. 
  NDSolve[{2 y'[r] + r  y''[r] == -.262468*(-13.60 r + 14.3996)*y[r] ,
      y[0.0001] == 1, y'[10] == 0}, y, {r, .000000001, 10}][[1]]

Plot[sol[r], {r, .000000001, .0001}]

enter image description here


DSolve is an exact solver, and exact solvers sometimes cannot solve equations with inexact (floating-point) coefficients because round-off error makes things that should be equal or cancel fail to do so. Use exact input and the system can be solved (after all, it's linear).

sol1 = DSolve[
      2*y'[r] + r*y''[r] == -.262468*(-13.60 r + 14.3996)*y[r],
      y[0.0001] == 1, y'[30] == 0},
    y, r];

Plot[Evaluate[y[r] /. sol1], {r, .000000001, .0001}]

enter image description here

Generic solution, followed by specialization to OP's case:

sol2 = DSolve[
   {2*y'[r] + r*y''[r] == c*(m r + b)*y[r], y[r1] == 1, y'[r2] == 0},
   y, r];

Block[{c, m, b, r1, r2},
 c = -.262468;
 m = -13.60;
 b = 14.3996;
 r1 = 0.0001;
 r2 = 30;
 Plot[Evaluate[y[r] /. sol2], {r, .000000001, .0001}]

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.