Save LD matrix as a sparse matrix

Converting LD matrices to sparse format reduces file size by half.

saveSparse(LD_matrix, LD_path, verbose = T)

See also

Other LD: LD_1KG_download_vcf(), LD_1KG(), LD_custom(), LD_ukbiobank(), compute_LD(), filter_LD(), get_locus_vcf_folder(), ldlinkr_ldproxy_batch(), load_or_create(), plot_LD(), popDat_1KGphase1, popDat_1KGphase3, rds_to_npz(), save_LD_matrix(), snpstats_get_MAF(), translate_population()