Re: maple and fsolve : not good, big bad bug.


plouffe schrieb:

Hello,

Have you ever tried to solve a trans. equation like cos(x) - x = 0 ?

for that one the real solution is neat and fast to compute :

BUT, others are kind of more difficult, at least for Maple.

For example : -3+cosh(x)-sinh(x)/tanh(x) = 0

the solution found will depend on the number of Digits,
unfortunately, the solution varies with the number of digits too.

If Digits = 128, then the solution found is
-99003.0000
when Digits = 64 , then the result is :
329999.0000000000000000000000000000000000000000000000000000000000...

in both cases it is false.

I have a whole plethora of equations like that,

does someone has a way to solve these equations ?

NOTE : mathematica is not any better.


Derive has no problem detecting the absence of solutions when instructed
to solve the equation -3+cosh(x)-sinh(x)/tanh(x) = 0 symbolically.

I suppose you instructed Maple to find a solution numerically, and
without specifying a search interval. I imagine the search will probe
the left-hand side at the requested precision, until the constant 3
drops below the least significant digit. For unknown reasons (we don't
know the search strategy), with Digits = 128 on Maple this seems to
happen for cosh(-99003.0000) = 1.430743797 10^42996, whence x =
-99003.0000 is - quite correctly - returned for a solution.

I haven't waited for Derive's numerical solver to terminate with this
equation, but I suspect that here too something will break sooner or
later.

Martin.
.

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