import _nnls
from numpy import asarray_chkfinite, zeros, double, require

def nnls(A,b):
    """ 
          Solve  || Ax - b ||_2 -> min  with  x>=0 

          Inputs:
                    A     --   matrix as above
                    b     --   vector as above

          Outputs:
                    x     --   solution vector
                    rnorm --  residual || Ax-b ||_2

    """

    A,b = map(asarray_chkfinite, (A,b))


    if A.ndim != 2:
        raise ValueError, "expected matrix"
    if b.ndim != 1:
        raise ValueError, "expected vector"

    m,n = A.shape

    if m != b.shape[0]:
        raise ValueError, "incompatible dimensions"

    A = require(A, double, [ "F" ])
    b = require(b, double)
    x,rnorm,mode =  _nnls.nnls(A,b)

    if mode != 1: raise RuntimeError, "too many iterations"

    return x, rnorm