Crash when computing the absorption with methods other than 'diag'

[alejandrojuria]

The Xatu executable crashes when it has to compute the absorption after the BSE calculation. For instance, the following command crashes:
./bin/xatu models/hBN.model excitonconfig/hBN_spinless.txt -a -m sparse
./bin/xatu models/hBN.model excitonconfig/hBN_spinless.txt -a -m davidson

It crashes with the following error:

xatu(8240,0x1fa956080) malloc: *** error for object 0xc649b1b: pointer being freed was not allocated
xatu(8240,0x1fa956080) malloc: *** set a breakpoint in malloc_error_break to debug

Most likely this is produced by a mismatch between the dimension of the matrix storing the eigenvectors (which for those methods is restricted to the number of states specified in the CLI, 8 by default), and the routine for the absorption, which expects the whole spectrum currently.