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More efficient setup of diagonal matrices #570

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Jul 18, 2025
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More efficient setup of diagonal matrices #570

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10 changes: 4 additions & 6 deletions pySDC/helpers/spectral_helper.py
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Original file line number Diff line number Diff line change
Expand Up @@ -312,14 +312,13 @@ def get_conv(self, name, N=None):
'''
N = N if N else self.N
sp = self.sparse_lib
xp = self.xp

def get_forward_conv(name):
if name == 'T2U':
mat = (sp.eye(N) - sp.diags(xp.ones(N - 2), offsets=+2)).tocsc() / 2.0
mat = (sp.eye(N) - sp.eye(N, k=2)).tocsc() / 2.0
mat[:, 0] *= 2
elif name == 'D2T':
mat = sp.eye(N) - sp.diags(xp.ones(N - 2), offsets=+2)
mat = sp.eye(N) - sp.eye(N, k=2)
elif name[0] == name[-1]:
mat = self.sparse_lib.eye(self.N)
else:
Expand Down Expand Up @@ -585,9 +584,8 @@ def get_Dirichlet_recombination_matrix(self):
'''
N = self.N
sp = self.sparse_lib
xp = self.xp

return sp.eye(N) - sp.diags(xp.ones(N - 2), offsets=+2)
return sp.eye(N) - sp.eye(N, k=2)


class UltrasphericalHelper(ChebychevHelper):
Expand Down Expand Up @@ -632,7 +630,7 @@ def get_S(self, lmbda):

if lmbda == 0:
sp = scipy.sparse
mat = ((sp.eye(N) - sp.diags(np.ones(N - 2), offsets=+2)) / 2.0).tolil()
mat = ((sp.eye(N) - sp.eye(N, k=2)) / 2.0).tolil()
mat[:, 0] *= 2
else:
sp = self.sparse_lib
Expand Down