# Why DSolve doesn't handle duplicate boundary condition

This code works well.

DSolve[{y''[x] + 10 y'[x] == 0, y == 0}, y[x], x]
(*{{y[x] -> 1/10 E^(-10 x) (-1 + E^(10 x)) C}}*)


But why mma gives warnings when I add one duplicate condition?

DSolve[{y''[x] + 10 y'[x] == 0, y == 0, y == 0}, y[x], x]


DSolve::bvsing: Unable to resolve some of the arbitrary constants in the general solution using the given boundary conditions. It is possible that some of the conditions have been specified at a singular point for the equation. >>

{{y[x] -> 1/10 E^(-10 x) (-1 + E^(10 x)) C}}


I notice that this code doesn't give warnings though there are duplicate conditions:

DSolveValue[{10 y'[x] == 10, y == 1, y == 1}, y[x], x]
(*{{y[x] -> 1 + x}}*)


Could I conclude that mma never deletes duplicate conditions while evaluating?

• interesting observation, but it is just a warning. You could do Quiet@DSolve ... – george2079 Jun 12 '15 at 14:14
• By trial and error, I have observed that this warning message occurs if and only if the number of BCs equals the order of the equation and one or more of the BCs are redundant. For instance, the error message occurs for DSolve[{y''''[x] == 0, y'' == 0, y' == 0, y == 0, y + y' == 0}, y[x], x] but not for DSolve[{y''''[x] == 0, y'' == 0, y'' == 0, y' == 0, y == 0, y + y' == 0}, y[x], x] or DSolve[{y''''[x] == 0, y' == 0, y == 0, y + y' == 0}, y[x], x]. – bbgodfrey Jun 13 '15 at 4:25

As of Version 10.3, the DSolve::bvsing warning is no longer emitted for
DSolve[{y''[x] + 10 y'[x] == 0, y == 0, y == 0}, y[x], x]