def build_sr(ll=None,dl=None,ul=None):
'''
Build a bsr or csr matrix by lower/diagonal/upper part of a tridiagonal matrix.
ll/dl/ul:
The lower/diagonal/upper part of tridiagonal matrix.
Leave None to make any of them zeros(no all of them).
*return*:
a csr_matrix instance for scalar version, else a bsr_matrix instance.
'''
nzarr=None
for i,il in enumerate([ll,ul,dl]):
if il is not None:
nzarr=il
n=len(il)+1 if i!=2 else len(il)
break
if nzarr is None:
raise ValueError('At least one of ll,dl,ul should be nonzeros!')
is_scalar=ndim(nzarr)==1
p=1 if is_scalar else nzarr.shape[-1]
if is_scalar:
mgen=csr_matrix
nullval=zeros(0)
else:
mgen=bsr_matrix
nullval=zeros([0,p,p])
indx_d=arange(n)
indx=concatenate([[] if dl is None else indx_d,[] if ll is None else indx_d[1:],[] if ul is None else indx_d[:-1]],axis=0)
indy=concatenate([[] if dl is None else indx_d,[] if ll is None else indx_d[:-1],[] if ul is None else indx_d[1:]],axis=0)
data=concatenate([nullval if dl is None else dl,nullval if ll is None else ll,nullval if ul is None else ul],axis=0)
odl=argsort(indx)
L=mgen((data[odl],indy[odl],ind2ptr(indx[odl],n)),dtype=nzarr.dtype)
return L
def tobsr(self):
'''Transform to bsr_matrix.'''
n=self.n
p=self.p
m=ndarray((n,n),dtype='O')
indx=concatenate([arange(n-1),arange(n),arange(1,n)])
indy=concatenate([arange(1,n),arange(n),arange(n-1)])
args=argsort(indx)
data=concatenate([self.upper,self.diagonal,self.lower])
res=bsr_matrix((data[args],indy[args],ind2ptr(indx[args],n)),blocksize=(p,p))
return res
