In TFOCS I’m minimizing the L1 norm of the *derivative* of x. So the argument looks like ||Dx|| where **D** is the derivative matrix and the norm is L1. So I decided to make a new nonsmooth function *prox_l1_d.m* based upon the *prox_l1.m* script already in TFOCS.

So take a look at *prox_l1.m*: I change the input argument **q** (and all it’s subsequent occurrences) to **D** (not strictly necessary…but it keeps my head clear), comment out the nargin stuff, and change line 41 from,

v = norm( qq(:).*x(:), 1 );

to

v = norm( qq*x(:), 1 );

But I have no idea what to do about lines 44-48 as I don’t understand the idea of a proximal function. So I have two questions:

**Is this a good way to implement L1 minimization of the derivative of x in TFOCS?**

**How do I change lines 44-48 to make it work?**

Thanks bunches,

Will