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我正在嘗試使用Cython來包裝LAPACK函數dgtsv（三方對稱方程組的求解器）。使用Cython包裝LAPACKE函數
我碰到了this previous answer，但由於dgtsv不是包裝在scipy.linalg中的LAPACK函數，我不認爲我可以使用這種特殊方法。相反，我一直在努力遵循this example。
這是我的lapacke.pxd文件的內容：
ctypedef int lapack_int
cdef extern from "lapacke.h" nogil:
int LAPACK_ROW_MAJOR
int LAPACK_COL_MAJOR
lapack_int LAPACKE_dgtsv(int matrix_order,
lapack_int n,
lapack_int nrhs,
double * dl,
double * d,
double * du,
double * b,
lapack_int ldb)
...這裏是我的薄用Cython包裝在_solvers.pyx：
#!python
cimport cython
from lapacke cimport *
cpdef TDMA_lapacke(double[::1] DL, double[::1] D, double[::1] DU,
double[:, ::1] B):
cdef:
lapack_int n = D.shape[0]
lapack_int nrhs = B.shape[1]
lapack_int ldb = B.shape[0]
double * dl = &DL[0]
double * d = &D[0]
double * du = &DU[0]
double * b = &B[0, 0]
lapack_int info
info = LAPACKE_dgtsv(LAPACK_ROW_MAJOR, n, nrhs, dl, d, du, b, ldb)
return info
...這是一個Python封裝和測試腳本：
import numpy as np
from scipy import sparse
from cymodules import _solvers
def trisolve_lapacke(dl, d, du, b, inplace=False):
if (dl.shape[0] != du.shape[0] or dl.shape[0] != d.shape[0] - 1
or b.shape != d.shape):
raise ValueError('Invalid diagonal shapes')
if b.ndim == 1:
# b is (LDB, NRHS)
b = b[:, None]
# be sure to force a copy of d and b if we're not solving in place
if not inplace:
d = d.copy()
b = b.copy()
# this may also force copies if arrays are improperly typed/noncontiguous
dl, d, du, b = (np.ascontiguousarray(v, dtype=np.float64)
for v in (dl, d, du, b))
# b will now be modified in place to contain the solution
info = _solvers.TDMA_lapacke(dl, d, du, b)
print info
return b.ravel()
def test_trisolve(n=20000):
dl = np.random.randn(n - 1)
d = np.random.randn(n)
du = np.random.randn(n - 1)
M = sparse.diags((dl, d, du), (-1, 0, 1), format='csc')
x = np.random.randn(n)
b = M.dot(x)
x_hat = trisolve_lapacke(dl, d, du, b)
print "||x - x_hat|| = ", np.linalg.norm(x - x_hat)
不幸的是，test_trisolve只是se grup打電話給_solvers.TDMA_lapacke。 我很確定我的setup.py是正確的 - ldd _solvers.so顯示_solvers.so正在運行時鏈接到正確的共享庫。
我不太確定如何從這裏開始 - 任何想法？
的簡要更新：
因爲我往往不會立即得到段錯誤的n較小的值，但我得到的廢話結果（|| X - x_hat ||應該是非常接近0）：
In [28]: test_trisolve2.test_trisolve(10)
0
||x - x_hat|| = 6.23202576396
In [29]: test_trisolve2.test_trisolve(10)
-7
||x - x_hat|| = 3.88623414288
In [30]: test_trisolve2.test_trisolve(10)
0
||x - x_hat|| = 2.60190676562
In [31]: test_trisolve2.test_trisolve(10)
0
||x - x_hat|| = 3.86631743386
In [32]: test_trisolve2.test_trisolve(10)
Segmentation fault
通常LAPACKE_dgtsv返回代碼爲0（應該指示成功），但偶爾我得到-7，這意味着參數7（b）具有非法值。發生的是隻有b的第一個值實際上正在修改。如果我繼續撥打test_trisolve，即使n很小，我也會最終遇到段錯誤。