# Plot a DifferentialRoot?

Posted 5 months ago
574 Views
|
3 Replies
|
1 Total Likes
|
 I have a problem with DifferentialRoot command. I am trying to solve certain ODE by DSolve and the solution is given as DifferentialRoot expression. Unfortunately when I try to work with it I obtain an error written below in the example.I have traced the problem to this simplified question. When I execute the following Plot[DifferentialRoot[Function[{y, x}, {-y''[x] + y[x] == 0, y == 3, y' == 1}]][x], {x, 0, 1}] I obtain plot of the solution to this equation. However when I change the coefficient in the equation to Plot[DifferentialRoot[Function[{y, x}, {-y''[x] +0.5 y[x] == 0, y == 3, y' == 1}]][x], {x, 0, 1}] I obtain an empty plot. Executing the command DifferentialRoot[Function[{y, x}, {-y''[x] +0.5 y[x] == 0, y == 3, y' == 1}]] leads to the following error DifferentialRoot::ieqn: The supplied equation in Function[{y,x},{-(<<<<1>>>>^(<<<<1>>>>))[<<<<1>>>>]+0.5 y[<<<<1>>>>]==0,y==3,(y^\[Prime])==1}] is not a linear differential equation with polynomial coefficients.** **DifferentialRoot::ifprec: Parameters in DifferentialRoot[Function[{y,x},{-(<<1>>^(<<1>>))[<<1>>]+0.5 y[<<1>>]==0,y==3,(y^\[Prime])==1}]] are not exact numbers. Does anyone have any suggestion what the problem is? Both equation are perfectly well defined solvable second order linear ODE. I have attached the file of the example. Attachments: Answer
3 Replies
Sort By:
Posted 5 months ago
 Error messages says, you don't uses exact numbers(polynomial coefficients).Use: 1/2 not 0.5.  Plot[DifferentialRoot[ Function[{y, x}, {-y''[x] + 1/2*y[x] == 0, y == 3, y' == 1}]][x], {x, 0, 1}] Then works. Answer
Posted 5 months ago
 Thank you for the reply. Do I understand it correctly that if I would like to have coefficients which are not whole numbers I always need to use Rationalize enviroment for them? Answer
Posted 5 months ago
 Yes.Use: Rationalize[0.5, 0] (*1/2*) Answer