How to get L1-norm of the Vector?

Hello,
Now I initialize a PSVector with 5 \*10 (rows*dims) by stating
`val den = PSVector.dense(10,5);`
`val local = den.pull(0);`
`local.norm()` -- the output result shows that norm() is to calculate the L2-norm of the first row of the pulled vector local.
Could you please teach me how to implement calculating the L1-norm of a vector. Thanks a lot.