Banded system solution from C using LAPACK DGBSV
I tried to find a similar thread related to this topic, but no one seems to care about tape systems (...)
I am interested in a strip pass matrix solution using LAPACK / ScaLAPACK from C code. First, I want to achieve a consistent solution using LAPACK before trying to do anything with ScaLAPACK.
Problem. The difference between row and column for both languages affects the process of my solution. Here's the system I intend to solve:
The following code converts this matrix to the LAPACK data structure specified in here .
int rr = 6; // Rank.
int kl = 2; // Number of lower diagonals.
int ku = 1; // Number of upper diagonals.
int nrhs = 1; // Number of RHS.
double vals[36] = {0.0, 0.0, 0.0, 0.0, 0.0, 0.0, // Req. ex. space.
0.0, 0.0, 0.0, 0.0, 0.0, 0.0, // Req. ex. space.
666.0, 0.0, 0.0, 0.0, 0.0, 22.5, // First up diag.
1.0, -50.0, -50.0, -50.0, -50.0, -2.6, // Main diagonal.
27.5, 27.5, 27.5, 27.5, 4.0, 666.0, // First low diag.
0.0, 0.0, 0.0, -1.0, 666.0, 666.0}; // 2nd low diag.
int lda = rr; // Leading dimension of the matrix.
int ipiv[6]; // Information on pivoting array.
double rhs[] = {1.0, 1.0, 1.0, 1.0, 1.0, 0.0}; // RHS.
int ldb = lda; // Leading dimension of the RHS.
int info = 0; // Evaluation variable for solution process.
int ii; // Iterator.
int jj; // Iterator.
dgbsv_(&rr, &kl, &ku, &nrhs, vals, &lda, ipiv, rhs, &ldb, &info);
printf("info = %d\n", info);
for (ii = 0; ii < ldb; ii++) {
printf("%f\n", rhs[ii]);
}
putchar('\n');
As I said, I am concerned that the way I was translating my matrix is wrong given the col-major nature as well as the indexed nature of Fortran as my solution gives:
[ejspeiro@node01 lapack-ex02]$ make runs
`pwd`/blogs < blogs.in
info = 1
1.000000
1.000000
1.000000
1.000000
1.000000
0.000000
The return value from Fortran info = 1
implies that the factorization is complete, but U(1,1) = 0
in the LU factorization A = LU
.
Any help is more than welcome.
Thanks, advanced!
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Ok, I'll answer this to call it "solvable".
These files are functional code. I'm making it available, if someone has the same problem: decision striped system of equations using LAPACK with the C .
And if anyone has any additional implementation suggestions, I would gladly welcome them!
My next step is to distribute the underlying matrices to be solved with ScaLAPACK.
Thank!
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As you noticed, your matrix was entered in string format. By writing it in column major, the lines that we will visually match the columns:
double vals[36] = {0.0, 0.0, 0.0, 1.0, 27.5, 0.0,
0.0, 0.0, 0.0, -50.0, 27.5, 0.0,
0.0, 0.0, 22.5, -50.0, 27.5, 0.0,
0.0, 0.0, 22.5, -50.0, 27.5, -1.0,
0.0, 0.0, 22.5, -50.0, 4.0, 0.0,
0.0, 0.0, 22.5, -2.6, 0.0, 0.0};
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