I have simple BVP for which one of boundaries is given as "L". My attempts to solve it gives various errors. One of the last attempts clearly shows that Maple "thinks" that L is rather another variable than unknown constant.
de := diff(y(x), x$4)-lambda*y(x) = 0;
sol:=dsolve({de,y(0)=0,(D@@2)(y)(0)=0, y(L)=0,(D@@2)(y)(L)=0}) assuming lambda<0;
What can I do?
The basic help page for the dsolve command is pretty clear on this.
See the second Calling Sequence example at top, where y(x) is supplied in the second argument.
The Parameters section, immediately below that, describes that second argument thusly:
y(x) - any indeterminate function of one variable, or a set or list of them,
representing the unknowns of the ODE problem
And so that is how you can specify which are the dependent and independent variables. Eg,
de := diff(y(x), x$4)-lambda*y(x) = 0:
sol := dsolve( {de, y(0)=0, (D@@2)(y)(0)=0, y(L)=0, (D@@2)(y)(L)=0},
{y(x)} ) assuming lambda<0;