[petsc-users] PetscArraycpy only copies half of the entries of the matrix rows

Roland Richter roland.richter at ntnu.no
Thu Dec 17 05:59:47 CST 2020 

Dear all,

I wanted to use PetscArraycpy for copying a part of one complex matrix A
with a row length of a_len and an offset of a_off into another matrix B
with a row length of b_len (smaller than a_len - a_off), using the
following code snippet:

/        PetscScalar *A_ptr, *B_ptr;//
//        MatDenseGetArray(A, &A_ptr);//
//        MatDenseGetArray(B, &B_ptr);//
//        MatView(A, PETSC_VIEWER_STDOUT_WORLD);//
//        for(size_t i = 0; i < num_local_rows; ++i) {//
//            PetscArraycpy(B_ptr + i * b_len, (2 * a_off + A_ptr) + i *
a_len, b_len);//
//        }/

/        MatAssemblyBegin(B, MAT_FINAL_ASSEMBLY);//
//        MatAssemblyEnd(B, MAT_FINAL_ASSEMBLY);//
//        MatView(B, PETSC_VIEWER_STDOUT_WORLD);/

When printing the first row of matrix A (with a_len = 128, a_off = 76
and b_len = 26), I get

/0.0000000000000000e+00 + 0.0000000000000000e+00i 0.0000000000000000e+00
+ 0.0000000000000000e+00i 0.0000000000000000e+00 +
0.0000000000000000e+00i -0.0000000000000000e+00 +
0.0000000000000000e+00i 0.0000000000000000e+00 + 0.0000000000000000e+00i
0.0000000000000000e+00 + 0.0000000000000000e+00i -0.0000000000000000e+00
+ 0.0000000000000000e+00i 0.0000000000000000e+00 +
0.0000000000000000e+00i 0.0000000000000000e+00 + 0.0000000000000000e+00i
0.0000000000000000e+00 + 0.0000000000000000e+00i 0.0000000000000000e+00
+ 0.0000000000000000e+00i -0.0000000000000000e+00 +
0.0000000000000000e+00i 0.0000000000000000e+00 + 0.0000000000000000e+00i
0.0000000000000000e+00 + 0.0000000000000000e+00i 0.0000000000000000e+00
+ 0.0000000000000000e+00i 0.0000000000000000e+00 +
0.0000000000000000e+00i 0.0000000000000000e+00 + 0.0000000000000000e+00i
0.0000000000000000e+00 + 0.0000000000000000e+00i -0.0000000000000000e+00
+ 0.0000000000000000e+00i 0.0000000000000000e+00 +
0.0000000000000000e+00i 0.0000000000000000e+00 + 0.0000000000000000e+00i
-0.0000000000000000e+00 + 0.0000000000000000e+00i 0.0000000000000000e+00
+ 0.0000000000000000e+00i 0.0000000000000000e+00 +
0.0000000000000000e+00i 0.0000000000000000e+00 + 0.0000000000000000e+00i
0.0000000000000000e+00 + 0.0000000000000000e+00i -0.0000000000000000e+00
+ 0.0000000000000000e+00i 0.0000000000000000e+00 +
0.0000000000000000e+00i 0.0000000000000000e+00 + 0.0000000000000000e+00i
0.0000000000000000e+00 + 0.0000000000000000e+00i 0.0000000000000000e+00
+ 0.0000000000000000e+00i 0.0000000000000000e+00 +
0.0000000000000000e+00i -0.0000000000000000e+00 +
0.0000000000000000e+00i 0.0000000000000000e+00 + 0.0000000000000000e+00i
0.0000000000000000e+00 + 0.0000000000000000e+00i -0.0000000000000000e+00
+ 0.0000000000000000e+00i 0.0000000000000000e+00 +
0.0000000000000000e+00i 0.0000000000000000e+00 + 0.0000000000000000e+00i
0.0000000000000000e+00 + 0.0000000000000000e+00i 0.0000000000000000e+00
+ 0.0000000000000000e+00i 0.0000000000000000e+00 +
0.0000000000000000e+00i -0.0000000000000000e+00 +
0.0000000000000000e+00i 0.0000000000000000e+00 + 0.0000000000000000e+00i
0.0000000000000000e+00 + 0.0000000000000000e+00i 0.0000000000000000e+00
+ 0.0000000000000000e+00i 0.0000000000000000e+00 +
0.0000000000000000e+00i -0.0000000000000000e+00 +
0.0000000000000000e+00i 0.0000000000000000e+00 + 0.0000000000000000e+00i
0.0000000000000000e+00 + 0.0000000000000000e+00i -0.0000000000000000e+00
+ 0.0000000000000000e+00i 0.0000000000000000e+00 +
0.0000000000000000e+00i 0.0000000000000000e+00 + 0.0000000000000000e+00i
-0.0000000000000000e+00 + 0.0000000000000000e+00i 0.0000000000000000e+00
+ 0.0000000000000000e+00i 0.0000000000000000e+00 +
0.0000000000000000e+00i -0.0000000000000000e+00 +
0.0000000000000000e+00i 0.0000000000000000e+00 + 0.0000000000000000e+00i
0.0000000000000000e+00 + 0.0000000000000000e+00i 0.0000000000000000e+00
+ 0.0000000000000000e+00i 0.0000000000000000e+00 +
0.0000000000000000e+00i 0.0000000000000000e+00 + 0.0000000000000000e+00i
0.0000000000000000e+00 + 0.0000000000000000e+00i 0.0000000000000000e+00
+ 0.0000000000000000e+00i -0.0000000000000000e+00 +
0.0000000000000000e+00i 0.0000000000000000e+00 + 0.0000000000000000e+00i
0.0000000000000000e+00 + 0.0000000000000000e+00i -0.0000000000000000e+00
+ 0.0000000000000000e+00i 0.0000000000000000e+00 +
0.0000000000000000e+00i 0.0000000000000000e+00 + 0.0000000000000000e+00i
0.0000000000000000e+00 + 0.0000000000000000e+00i 0.0000000000000000e+00
+ 0.0000000000000000e+00i -0.0000000000000000e+00 +
0.0000000000000000e+00i 0.0000000000000000e+00 + 0.0000000000000000e+00i
0.0000000000000000e+00 + 0.0000000000000000e+00i 0.0000000000000000e+00
+ 0.0000000000000000e+00i 0.0000000000000000e+00 +
0.0000000000000000e+00i -0.0000000000000000e+00 +
0.0000000000000000e+00i -7.5118186821231378e-02 +
-1.2515848507502547e-01i 5.7593629917958706e+00 +
1.6535197175842331e+00i -6.3062119866941906e+01 +
3.2118985283369987e+01i 1.6228535942636518e+02 +
-4.4588492144691378e+02i 8.7350162264986420e+02 +
2.0568440963147814e+03i -7.4258479521622921e+03 +
-3.3031631388498363e+03i 2.2699374989663269e+04 +
-7.8289291098031481e+03i -2.7846379282467926e+04 +
5.2456793075148809e+04i -3.2554674832896777e+04 +
-1.2108819252524960e+05i 1.9430868047197413e+05 +
1.2114559011378702e+05i -3.5831799834334152e+05 +
7.0086227392363056e+04i 3.0028983479603863e+05 +
-4.1447894788669585e+05i 7.8224949502036819e+04 +
6.2926756374162808e+05i -5.3474873053744854e+05 +
-4.4718914789259754e+05i 6.8111038372267899e+05 +
-3.6947593166740131e+04i -4.1287212326113920e+05 +
4.2925417635846150e+05i 7.1098224367113344e+03 +
-4.6490743916366581e+05i 2.1807010096419850e+05 +
2.4106178223450572e+05i -2.0304162108015743e+05 +
-1.7254769976182859e+04i 9.0164628688356752e+04 +
-7.0830186001321214e+04i -8.9050769071193699e+03 +
5.7267241933255813e+04i -1.4789632694550470e+04 +
-2.1786332309775924e+04i 1.0491004489879153e+04 +
2.3873712516742830e+03i -3.4183915782335853e+03 +
1.9886861075931499e+03i 3.7807432692260045e+02 +
-1.2521184263406540e+03i 0.0000000000000000e+00 +
0.0000000000000000e+00i 0.0000000000000000e+00 + 0.0000000000000000e+00i
0.0000000000000000e+00 + 0.0000000000000000e+00i -0.0000000000000000e+00
+ 0.0000000000000000e+00i 0.0000000000000000e+00 +
0.0000000000000000e+00i 0.0000000000000000e+00 + 0.0000000000000000e+00i
-0.0000000000000000e+00 + 0.0000000000000000e+00i 0.0000000000000000e+00
+ 0.0000000000000000e+00i 0.0000000000000000e+00 +
0.0000000000000000e+00i 0.0000000000000000e+00 + 0.0000000000000000e+00i
0.0000000000000000e+00 + 0.0000000000000000e+00i -0.0000000000000000e+00
+ 0.0000000000000000e+00i 0.0000000000000000e+00 +
0.0000000000000000e+00i 0.0000000000000000e+00 + 0.0000000000000000e+00i
-0.0000000000000000e+00 + 0.0000000000000000e+00i 0.0000000000000000e+00
+ 0.0000000000000000e+00i 0.0000000000000000e+00 +
0.0000000000000000e+00i -0.0000000000000000e+00 +
0.0000000000000000e+00i 0.0000000000000000e+00 + 0.0000000000000000e+00i
0.0000000000000000e+00 + 0.0000000000000000e+00i 0.0000000000000000e+00
+ 0.0000000000000000e+00i 0.0000000000000000e+00 +
0.0000000000000000e+00i 0.0000000000000000e+00 + 0.0000000000000000e+00i
0.0000000000000000e+00 + 0.0000000000000000e+00i 0.0000000000000000e+00
+ 0.0000000000000000e+00i 0.0000000000000000e+00 + 0.0000000000000000e+00i/

and for the first row of B I get

/-0.0000000000000000e+00 + 0.0000000000000000e+00i
-7.5118186821231378e-02 + -1.2515848507502547e-01i
5.7593629917958706e+00 + 1.6535197175842331e+00i -6.3062119866941906e+01
+ 3.2118985283369987e+01i 1.6228535942636518e+02 +
-4.4588492144691378e+02i 8.7350162264986420e+02 +
2.0568440963147814e+03i -7.4258479521622921e+03 +
-3.3031631388498363e+03i 2.2699374989663269e+04 +
-7.8289291098031481e+03i -2.7846379282467926e+04 +
5.2456793075148809e+04i -3.2554674832896777e+04 +
-1.2108819252524960e+05i 1.9430868047197413e+05 +
1.2114559011378702e+05i -3.5831799834334152e+05 +
7.0086227392363056e+04i 3.0028983479603863e+05 +
-4.1447894788669585e+05i 0.0000000000000000e+00 +
0.0000000000000000e+00i 0.0000000000000000e+00 + 0.0000000000000000e+00i
0.0000000000000000e+00 + 0.0000000000000000e+00i 0.0000000000000000e+00
+ 0.0000000000000000e+00i 0.0000000000000000e+00 +
0.0000000000000000e+00i 0.0000000000000000e+00 + 0.0000000000000000e+00i
6.9004764357806349e-310 + 6.9004764357806349e-310i
6.9004764365446580e-310 + 6.9004764300000669e-310i
0.0000000000000000e+00 + 0.0000000000000000e+00i 0.0000000000000000e+00
+ 0.0000000000000000e+00i 0.0000000000000000e+00 +
0.0000000000000000e+00i 0.0000000000000000e+00 + 0.0000000000000000e+00i
0.0000000000000000e+00 + 0.0000000000000000e+00i/

Apparently, only 13 complex values have been copied, and not 26.
Moreover, if my source destination is chosen to be (a_off + A_ptr)
instead, I will just copy 0-values. When increasing the number of values
I would like to copy, nothing changes (except getting a segfault for
sufficient large values).

Why does that happen? And how can I copy all values into the second
matrix, and not only half of them?

Another question: Is there a parallel version of that function, to copy
all local rows in parallel, or do I have to write it myself, for example
by using OpenMP?

Thanks!

Roland



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