[petsc-users] difference between solns for np=1 and np>1.

[(Rebecca) Xuefei YUAN]

Dear all,

I have a piece of code working right for np=1, but when I use np>1(for  
example, np=2), the solution is different from the one with np=1.

I checked the residual function(f_np1_itsi vs f_np2_itsi) and Jacobian  
matrix(J_np1_itsi,J_np2_itsi), it turns out that for different initial  
guesses,

f_np1_its0 = f_np2_its0;
J_np1_its0 = J_np2_its0;

although two Jacobians are the same, they have different nonzero structures.

After 1 nonlinear iterations, the solution is not the same.

I do not understand that if I have F(u^{m}) and J(u^{m}) the same, how  
could I get different \delta u^{m} in np=1 and np=2 situations?

Thanks a lot!

Rebecca

-- 
(Rebecca) Xuefei YUAN
Department of Applied Physics and Applied Mathematics
Columbia University
Tel:917-399-8032
www.columbia.edu/~xy2102