c++ - Eigen Library:: How do I create a block diagonal sparse matrix out of existing sparse matrices? -

i have bunch of (n*n) sized sparse matrices called m1, m2... , mj.

i want create large block-diagonal sparse matrix looks this:

    |m1 0  0 . . . |     |0  m2 0 . . . |     |.  .  . . . . |     |.  .  . mj-1 0|     |0  0  0 ... mj| 

i tried following:

    eigen::sparsematrix<double> matblk(j*n,j*n);     matblk.reserve(eigen::vectorxd::constant(j*n,3);      //i know there @ 3 nonzero elements per row      matblk.topleftcorner(n,n) = m1.topleftcorner(n,n);     matblk.block(n,n,n,n) = m2.topleftcorner(n,n);     .     .     matblk(bottomrightcorner(n,n)) = mj.topleftcorner(n,n);     matblk.makecompressed(); 

this method not working. values in smaller matrices aren't getting copied larger block matrix. function:

    matblk.nonzeros()  

returns 0.

i new library. appreciated.

unfortunately looks can't assign sparse matrices in way due how inefficient resulting code be. forum post 2 years old seems things still same (https://forum.kde.org/viewtopic.php?f=74&t=112018)

you have assign entries 1 one, either direct assignment or triplets.

a.block(i,j,m,n) = b; 

becomes

for (int ii = i; ii < i+m; ++ii) {   (int jj = j; jj < j+n; ++jj) {     // direct assignment      a.insert(ii, jj) = b(ii - i, jj - j);      // triplets     triplets.push_back(triplet(ii, jj, b(ii-i,jj-j)));   } }