WOLFRAM

Wolfram Language & System Documentation Center
NDSolve::bdord NDSolveValue::bdord ParametricNDSolve::bdord ParametricNDSolveValue::bdord

NDSolve::bdord NDSolveValue::bdord ParametricNDSolve::bdord ParametricNDSolveValue::bdord

Details

  • This message is generated when the number of times that a function is differentiated with respect to a particular variable is greater in a boundary condition than in the differential equation.
  • Off[message] switches off the message; On[message] switches it on. For example: Off[NDSolve::bdord].

Examples

Basic Examples  (1)

The derivative boundary condition is specified with respect to the wrong variable:

Wolfram Language code: NDSolve[{Derivative[2, 0][f][x, t] == Derivative[0, 1][f][x, t], f[0, t] == Sin[t], f[x, 0] == 0, Derivative[0, 1][f][5, t] == 0}, f, {x, 0, 5}, {t, 0, 4 Pi}]

This shows a valid specification of a solution of this partial differential equation:

Wolfram Language code: sol = NDSolve[{Derivative[2, 0][f][x, t] == Derivative[0, 1][f][x, t], f[0, t] == Sin[t], f[x, 0] == 0, Derivative[1, 0][f][5, t] == 0}, f, {x, 0, 5}, {t, 0, 4 Pi}]

The problem is that is specifying the first derivative with respect to . However, the highest-order time derivative term in the equation is , so only a specification of the function can be given.

However, because of the term in the equations, you need a specification of both the value of the function and first derivative of the function. Therefore, if you change to , the proper number of boundary conditions is specified, so you can get a solution.

This shows a plot of the solution:

Wolfram Language code: Plot3D[Evaluate[f[x, t] /. sol[[1]]], {x, 0, 5}, {t, 0, 4 Pi}]

Clear the value of sol.

Wolfram Language code: Clear[sol]