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#588 a result of a differential equation is wrong

closed
nobody
None
5
2004-07-27
2004-07-22
Anonymous
No

the solution of the differential equation
(1+x)*'diff(y,x)+y=1+log(1+x); is %C/(1+x)+log(1+x).
The command ode2(%,y,x)returns the following solution
: y=((x+1)log(x+1)+%C-1)/(x+1). It looks like there's
an error of sign (with the -1 which multiplicate the
constant %C)

Discussion

  • Barton Willis
    Barton Willis
    2004-07-25

    Logged In: YES
    user_id=895922

    This is not a bug; both solutions are correct. In Maxima's
    solution substitute %c --> %c + 1. This makes the two
    solutions identical. Since %c is an arbitrary parameter, the
    substitution %c --> %c + 1 is okay.

    Suggestion: learn how to substitute a putative solution
    to an equation (DE or algebraic) into the equation to
    check if it is correct.

    Barton

     
  • Barton Willis
    Barton Willis
    2004-07-27

    • status: open --> closed