Possible serious bug : latexing an expression containing a held integral triggers its evaluation...

Emmanuel Charpentier

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Aug 9, 2020, 10:00:11 AM8/9/20

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Note : for once, this is a cross-post from ask.sagemath.org, for ticket advice…

Exploring this ask.sagemath question led me to discover what I think is a serious bug : it seems that latexing an expression containing a held (= unevaluated) integral triggers the latter’s evaluation ; ditto for viewing or showing…

Minimal case:

    sage: Ig=sin(x)
    sage: It=Ig.integrate(x,-pi,pi,hold=True)
    sage: Cs=1/(2*pi)
    sage: latex(It)
    \int_{-\pi}^{\pi} \sin\left(x\right)\,{d x}

So far, so good. But :

    sage: Ex=Cs*It
    sage: Ex
    1/2*integrate(sin(x), x, -pi, pi)/pi
    sage: latex(Ex)
    \frac{0}{2 \, \pi}

Aaaarghh ! And, of course :

    sage: show(Ex)
    \newcommand{\Bold}[1]{\mathbf{#1}}\frac{0}{2 \, \pi}

And view(Ex) proudly displays this crap…

IMHO, this is a serious bug, entailing a risk of inadvertently triggering long, impossible or never ending computations.

Unless someone points me to the direction and magnitude of my stupidity, I intend to file this as a critical (maybe blocker) ticket; however, the target is not clear to me : I do not thoink that the rendering system is the only culprit (nor even the main one…) ; there may be a more fundamental problem in the evaluation system.

Advice ?

Emmanuel Charpentier

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Aug 9, 2020, 10:31:47 AM8/9/20

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The problem can be reproduced on [sagecell](https://sagecell.sagemath.org/?z=eJxVi0EKhDAMAO99SSKu4t5zEg-5-wFxQy2ILU1W8nx72cPCwMDAcKQ9KzgGNuI4pMsk1s0EvH-V1DeOfH5orV_BMCtNI7y7kjAsTrN2bKHUNsHZHgc2xL-weAu6RRluqZry9fMDXHAoTw==&lang=sage&interacts=eJyLjgUAARUAuQ==), which is currently at 9.1.

HTH,

Emmanuel Charpentier

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Aug 9, 2020, 11:38:10 AM8/9/20

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On Cocalc, I have checked that the problem can be reproduced on all available Sage kernels back to 8.2.

Looks more like an error from me, rather than a bug…

Suggestions most welcome !

Emmanuel Charpentier

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Aug 9, 2020, 11:53:40 AM8/9/20

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One more data point: calling latex (or show or view) on such an expression containing a held integral in a hold context gives a RecursionError.

HTH,

Emmanuel Charpentier

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Aug 10, 2020, 5:15:54 AM8/10/20

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This is now Trac#30326 (with priority major, but not critical, notwithstanding the potential for session/notebook crash or stalling).