25-Diamond I

Solved

Bug in symbolics in combination with floating point numbers

Forum|Forum|8 years ago
June 11, 2017
3 replies
5341 views

Did we already discuss that kind of bug here?

And has anybody an idea what the reason for this strange errror (recursive definition) could be?

The error occurs when the frequency is negative and floating point,

1_SymBug-xmcdz.zip

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Best answer by LucMeekes

Your memory is still OK. I guess this is where it was seen before:Recursive definition problem when extracting real part of equation.

Luc

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LucMeekes

23-Emerald IV

This is Mathcad 11:

How does Prime deal with it?

Luc

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Werner_E

Author

25-Diamond I

Could have bet on that it would work OK with Maple.

Prime suffers from the same bug (at least version 3.0).

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LucMeekes

23-Emerald IV

Check if there's a difference in solving sin(2 x), sin(-2 x), sin(2.0 x) and sin(-2.0 x), to see if Mathcad or Mupad handles those functions differently. Or do a series expansion.

Luc

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Werner_E

Author

25-Diamond I

Positive factors -> no problem. no matter how they are written

neagtive integers written without decimal point -> no problem

But when the factor is negative and is written with a decimal point, whatever I do symbolically with that expression, it will fail with that "recursive definition" error.

I'll try to get hold on a machine with an older release of MC15 or even MC14 to see, if the bug is already present there or was introduced later.

L

LucMeekes

23-Emerald IV

The 0 (zero) answer is too simple, what does 'solve fully' do? ( I don't have that in mathcad 11).

Luc

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LucMeekes

23-Emerald IV

Is this Symbolic Fourier Transform similar?

W

Werner_E

Author

25-Diamond I

LucMeekes wrote:

Is this Symbolic Fourier Transform similar?

Don't think so. Guess it wasn't a bug there. The OP used a wrong syntax for the "fourier" command and was not aware of the annoying effect that the symbolics switch to its "numeric/float" mode whenever just one number is written with a decimal point.

This auto-float mode could be part of the reason for the bug as expressions are dealt with and are evaluated differently when in float mode. But I see no reason why a recursive definition should be diagnosed just because the symbolics work in float mode.

I vaguely remember a thread dealing with a bug/problem concerning symbolics and floating point numbers. Just can't remember, nor find the thread.