def convertCRSIndex2Map(rowIdx, colPtr):
    """Converts CRS indices to uncompressed indices (row, col)."""
    ii = []
    jj = []
    for i in range(len(colPtr) - 1):
        for j in range(colPtr[i], colPtr[i + 1]):
            ii.append(i)
            jj.append(rowIdx[j])
    return ii, jj