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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?

Kelly Shepphard
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  • What is this!? Your inlined code does not show what you claim, because it is not valid Maple syntax and doesn't even make it past the parser. – acer Jan 13 '19 at 00:45
  • Sorry. I've edited it now so it "works" like was stated here. Probably I've posted earlier version of the code accidentally. – Kelly Shepphard Jan 13 '19 at 06:18

1 Answers1

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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;
acer
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