# What should I make of "Simplify: Time spent on a transformation exceeded -4.03955*10^12 seconds"?

Running version "12.0.0 for Microsoft Windows (64-bit) (April 6, 2019)", in case that matters. I fed Mathematica the command

Simplify[
Integrate[
e*Exp[-e*t]*F*Exp[-F *t]* Exp[-\[Lambda] - b*t]*
Integrate[
Sum[(b*s + \[Lambda])^y/y! *
Sum[2^(-y)*Binomial[y, z]*(b*(t - s))^(x - z)/(x - z)!, {z, 0, x}],
{y, 0, Infinity}],
{s, 0, t}],
{t, 0, Infinity}],
e > 0 && F > 0 && \[Lambda] > 0 && b > 0 && Element[x, Integers]]


(line breaks added for readability, though I don't think that matters). It output the warning message

Simplify::time: Time spent on a transformation exceeded -4.03955*10^12 seconds, and the transformation was aborted. Increasing the value of TimeConstraint option may improve the result of simplification.

In fact, it gave me that message three times, and then

General::stop: Further output of Simplify::time will be suppressed during this calculation.

Twelve hours after that, it gave me an answer. The warning bugs me for a couple of reasons. First, 4.03955*10^12 seconds is thousands of years. Second, I don't know what to make of the negative number of seconds. Third, when I Googled I didn't see any results about this. (The only results on this site that I found are all of the form "Time spent on a transformation exceeded 300 seconds", which is rather different.)

The number -4.03955*10^12 makes me think there's some type of overflow error going on, but I've got no idea other than that.

• Was this run on a fresh kernel? Commented Jun 2, 2021 at 7:51
• How long after running the command do you get the first error message? Commented Jun 2, 2021 at 17:38
• "Twelve hours after that, it gave me an answer." Did it give you "the correct answer" ?
– JimB
Commented Jun 2, 2021 at 21:12
• @N.J.Evans I don't know exactly because I went away to do other stuff, but I think the message had already appeared twice when I checked back 3 hours later. Commented Jun 3, 2021 at 12:27
• @JimB It gave me something which was equal to the input, yes. (Specifically it left the integrals and infinite sum alone, and replaced the inner sum with some HypergeometricU business. If any of you think it matters I'll edit the question to include the output.) Commented Jun 3, 2021 at 12:38

This is just an extended comment as it does not answer the specific question asked. My only guess to the specific question is that the double sum embedded in a double integral where one of the parameters (x) must be an integer confuses Mathematica. In addition, my limited imagination does not allow me to see how explaining the specific error message would help anyone. This extended comment provides a work-around for providing a general solution to the original equation (other than having to supply a specific integer value for x).

Sometimes it helps to break up the calculation into parts. First consider the double sum where all terms are left unknown except for x:

Table[{x, Sum[(b*s + λ)^y/y!*Sum[2^(-y)*Binomial[y, z]*(b*(t - s))^(x - z)/(x - z)!, {z, 0, x}],
{y, 0, Infinity}]}, {x, 8}] // FullSimplify // TableForm


So we can see a common structure and note that the integer divisors are of the form 2^x x! (using oeis.org). Now a function can be written for the double sum:

sum[x_, b_, s_, λ_, t_] := (-1)^x (b (s - 2 t) - λ)^x Exp[(b s + λ)/2]/(2^x x!)


Setting a value of x we can get a result:

x = 3;
Integrate[e*Exp[-e*t]*F*Exp[-F*t]*Exp[-λ - b*t]*
Integrate[sum[x, b, s, λ, t], {s, 0, t}], {t, 0, Infinity},
Assumptions -> {e > 0, F > 0, λ > 0, b > 0}] // FullSimplify


Maybe there's a common structure for integer values of x but I'll leave that up to you.

• While the Question's only question is in its title, this Answer completely fails to respond to that question: "What should I make of 'Simplify: Time spent on a transformation exceeded -4.03955*10^12 seconds'?". Commented Jun 2, 2021 at 13:17
• @EricTowers. I agree.
– JimB
Commented Jun 2, 2021 at 14:02
• @JimB The table stuff is a neat trick, though honestly I think I'm going to back up and try a different approach to my problem altogether. I'm still curious about the weird warning, but it seems like it might not be familiar to anyone here. Commented Jun 3, 2021 at 13:50

What should I make of "Simplify: Time spent on a transformation exceeded -4.03955*10^12 seconds"?

Good old bug.

>> dec2hex(int64(-4.03955*10^12))
ans = FFFFFC53780EA480


Looks like a signed 2s complement 64-bit integer that rolled over at some point. The timing calculation uses much smaller units, and the large negative value survived through the conversion to seconds.

Reminder to self: check whether they fixed it between 10.0 and 13.3.

* The travesty of showing this using Octave/Matlab instead of Mathematica is intentional of course.