how to quickly decompressed a matrix

I have compressed matrix a, first row is index and second row is value, how can i convert it to full matrix b of 2x10 elements below?

a = [1      5     8;
     0.2  0.6  -1.1];

b = [1     2   3   4   5   6   7    8    9   10;
     0.2 0.2 0.2 0.2 0.6 0.6 0.6 -1.1 -1.1 -1.1];

Answer 1

[Walter Roberson]

repelem using diff() of the indices as the counts

[Sam]

Thanks Walter