100 lines
2.8 KiB
Python
100 lines
2.8 KiB
Python
""" Functions that operate on sparse matrices
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"""
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from __future__ import division, print_function, absolute_import
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__all__ = ['count_blocks','estimate_blocksize']
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from .csr import isspmatrix_csr, csr_matrix
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from .csc import isspmatrix_csc
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from ._sparsetools import csr_count_blocks
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def extract_diagonal(A):
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raise NotImplementedError('use .diagonal() instead')
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#def extract_diagonal(A):
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# """extract_diagonal(A) returns the main diagonal of A."""
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# #TODO extract k-th diagonal
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# if isspmatrix_csr(A) or isspmatrix_csc(A):
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# fn = getattr(sparsetools, A.format + "_diagonal")
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# y = empty( min(A.shape), dtype=upcast(A.dtype) )
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# fn(A.shape[0],A.shape[1],A.indptr,A.indices,A.data,y)
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# return y
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# elif isspmatrix_bsr(A):
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# M,N = A.shape
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# R,C = A.blocksize
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# y = empty( min(M,N), dtype=upcast(A.dtype) )
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# fn = sparsetools.bsr_diagonal(M//R, N//C, R, C, \
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# A.indptr, A.indices, ravel(A.data), y)
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# return y
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# else:
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# return extract_diagonal(csr_matrix(A))
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def estimate_blocksize(A,efficiency=0.7):
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"""Attempt to determine the blocksize of a sparse matrix
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Returns a blocksize=(r,c) such that
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- A.nnz / A.tobsr( (r,c) ).nnz > efficiency
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"""
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if not (isspmatrix_csr(A) or isspmatrix_csc(A)):
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A = csr_matrix(A)
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if A.nnz == 0:
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return (1,1)
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if not 0 < efficiency < 1.0:
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raise ValueError('efficiency must satisfy 0.0 < efficiency < 1.0')
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high_efficiency = (1.0 + efficiency) / 2.0
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nnz = float(A.nnz)
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M,N = A.shape
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if M % 2 == 0 and N % 2 == 0:
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e22 = nnz / (4 * count_blocks(A,(2,2)))
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else:
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e22 = 0.0
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if M % 3 == 0 and N % 3 == 0:
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e33 = nnz / (9 * count_blocks(A,(3,3)))
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else:
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e33 = 0.0
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if e22 > high_efficiency and e33 > high_efficiency:
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e66 = nnz / (36 * count_blocks(A,(6,6)))
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if e66 > efficiency:
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return (6,6)
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else:
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return (3,3)
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else:
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if M % 4 == 0 and N % 4 == 0:
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e44 = nnz / (16 * count_blocks(A,(4,4)))
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else:
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e44 = 0.0
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if e44 > efficiency:
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return (4,4)
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elif e33 > efficiency:
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return (3,3)
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elif e22 > efficiency:
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return (2,2)
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else:
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return (1,1)
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def count_blocks(A,blocksize):
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"""For a given blocksize=(r,c) count the number of occupied
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blocks in a sparse matrix A
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"""
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r,c = blocksize
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if r < 1 or c < 1:
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raise ValueError('r and c must be positive')
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if isspmatrix_csr(A):
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M,N = A.shape
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return csr_count_blocks(M,N,r,c,A.indptr,A.indices)
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elif isspmatrix_csc(A):
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return count_blocks(A.T,(c,r))
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else:
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return count_blocks(csr_matrix(A),blocksize)
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