Code run in 5 minutes with V12 but runs forever with V13.3

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2

Setting WorkingPrecision to 10 is strange: it is less than MachinePrecision, which is 16. Let the WorkingPrecision be the default and it will be very fast.

I don’t know why the following takes forever in 13.3, but is fast in 12.0:

NIntegrate[E^(I (k + k^2)),
 {k, -10, 10},
 WorkingPrecision -> 10]

It may be a bug.

3

Thanks for your reply!

Using the default MachinePrecision, I get NIntegrate::errprec: Catastrophic loss of precision in the global error estimate due to insufficient WorkingPrecision or divergent integral.

This led me to try Method → “LevinRule”, which in fact is fast.

4

Is not the answer.

If your integral is from {k,-Infinity,Infinty} we can use a FourierTransform to compute integral.

    ClearAll["`*"]; Remove["`*"]

    F[k_] := 1/Sqrt[\[Pi] a] Sin[k a]/k;

    FourierTransform[F[k] Exp[I (k x - (\[HBar] k^2)/(2 m) t)]*Exp[-I k x] // Expand, k, x] // Simplify
  
   (*((1/4 + I/4) t^(3/2) \[HBar]^(
    3/2) (Erfi[((1/2 + I/2) Sqrt[m] (a - x))/(Sqrt[t] Sqrt[\[HBar]])] + 
      Erfi[((1/2 + I/2) Sqrt[m] (a + x))/(
       Sqrt[t] Sqrt[\[HBar]])]))/(Sqrt[a] m^(3/2) ((I t \[HBar])/m)^(3/2)
    )*)

then:

   Clear[Psiappx2]; 

   a = 1;
   m = 1;
   \[HBar] = 1;

   Psiappx2[x_, t_] := ((1/4 + I/4) t^(3/2) \[HBar]^(
     3/2) (Erfi[((1/2 + I/2) Sqrt[m] (a - x))/(Sqrt[t] Sqrt[\[HBar]])] + 
       Erfi[((1/2 + I/2) Sqrt[m] (a + x))/(Sqrt[t] Sqrt[\[HBar]])]))/(
    Sqrt[a] m^(3/2) ((I t \[HBar])/m)^(3/2));

   Plot3D[Abs[Psiappx2[x, t]]^2, {x, -5, 5}, {t, 0, 1}, PlotRange -> All,PlotPoints -> 100]

10023Bez tytułu.png
10023Bez tytułu.png835×705 178 KB

5

Indeed, my integral is {k,-Infinity,Infinty}, and Mariusz’s solution works even better, thank you!