Reference matrix:
    1.5    2.0    0.5    0.0    0.0
    2.5    5.0    3.5    0.5    0.0
    0.5    4.0   10.0    5.0    0.5
    0.0    0.5    5.5   17.0    6.5
    0.0    0.0    0.5    7.0   25.5
 sprstm matrix (off-diag. elements of mag >):  0.9900000    
    1.5    2.0    0.0    0.0    0.0
    2.5    5.0    3.5    0.0    0.0
    0.0    4.0   10.0    5.0    0.0
    0.0    0.0    5.5   17.0    6.5
    0.0    0.0    0.0    7.0   25.5