Advanced Search

Question: A small bug in pdsolve

Question:A small bug in pdsolve

Rouben Rostamian 7596 Maple 2020
bug pdsolve division-by-zero
October 19 2020
2

Here is a division-by-zero bug in a solution produced by pdsolve.  Admittedly, this sort of problem can be difficult to avoid in a CAS, but here it is, in case there is a chance to get it fixed somehow.

> 

restart;
> 

kernelopts(version);

`Maple 2020.1, X86 64 LINUX, Jul 30 2020, Build ID 1482634`

> 

pde := diff(u(x,y,t),t,t) = diff(u(x,y,t),x,x) + diff(u(x,y,t),y,y);

diff(diff(u(x, y, t), t), t) = diff(diff(u(x, y, t), x), x)+diff(diff(u(x, y, t), y), y)

> 

bc := u(x,0,t)=0, u(x,1,t)=0, u(0,y,t)=0, u(1,y,t)=0;

u(x, 0, t) = 0, u(x, 1, t) = 0, u(0, y, t) = 0, u(1, y, t) = 0

> 

ic := u(x,y,0) = x*y*sin(Pi*x)*sin(Pi*y),  D[3](u)(x,y,0)=0;

u(x, y, 0) = x*y*sin(Pi*x)*sin(Pi*y), (D[3](u))(x, y, 0) = 0

> 

pdsol := pdsolve({pde, bc, ic});

"pdsol:=u(x,y,t)=(&sum;) (&sum;)-(2 sin(n Pi x) sin(n1 Pi y) cos(Pi sqrt(n^2+n1^2) t) ({[[Pi^2,n=1],[-(8 n ((-1)^n+1))/((n-1)^2 (n+1)^2),1<n]]) n1 ((-1)^n1+1))/(Pi^4 (-1+n1)^2 (n1+1)^2)"

> 

eval(pdsol, infinity=4);
value(%);

"u(x,y,t)=(&sum;) (&sum;)-(2 sin(n Pi x) sin(n1 Pi y) cos(Pi sqrt(n^2+n1^2) t) ({[[Pi^2,n=1],[-(8 n ((-1)^n+1))/((n-1)^2 (n+1)^2),1<n]]) n1 ((-1)^n1+1))/(Pi^4 (-1+n1)^2 (n1+1)^2)"

Error, (in SumTools:-DefiniteSum:-ClosedForm) summand is singular in the interval of summation

 

 

 

Download pdsolve-bug.mw

 
Please Wait...