我正在尝试使用Python中的兰伯特函数来解决问题;但是,在使用 Canopy 时,我收到 NaN 响应。我的等式如下:
from scipy.special import lambertw
y=8.21016005323e+158
gama = -339.375260893
x = lambertw(y) + gama
print x
当我在 Matlab 中执行相同的代码时,我得到 x = 20.6524 的值,这就是我正在寻找的结果。
我不确定这个 NaN 值是由什么引起的,但我怀疑这可能与我对 y 的巨大值有关。有什么方法可以让Python来处理这个问题并给我正确的结果吗?
谢谢
scipy.show_config()
umfpack_info:
NOT AVAILABLE
lapack_opt_info:
libraries = ['mkl_lapack95_lp64', 'mkl_core_dll', 'mkl_intel_lp64_dll', 'mkl_intel_thread_dll']
library_dirs = ['C:\\Users\\vagrant\\src\\master-env\\libs']
define_macros = [('SCIPY_MKL_H', None)]
include_dirs = ['C:\\Users\\vagrant\\src\\master-env\\include']
blas_opt_info:
libraries = ['mkl_core_dll', 'mkl_intel_lp64_dll', 'mkl_intel_thread_dll']
library_dirs = ['C:\\Users\\vagrant\\src\\master-env\\libs']
define_macros = [('SCIPY_MKL_H', None)]
include_dirs = ['C:\\Users\\vagrant\\src\\master-env\\include']
openblas_info:
NOT AVAILABLE
lapack_mkl_info:
libraries = ['mkl_lapack95_lp64', 'mkl_core_dll', 'mkl_intel_lp64_dll', 'mkl_intel_thread_dll']
library_dirs = ['C:\\Users\\vagrant\\src\\master-env\\libs']
define_macros = [('SCIPY_MKL_H', None)]
include_dirs = ['C:\\Users\\vagrant\\src\\master-env\\include']
blas_mkl_info:
libraries = ['mkl_core_dll', 'mkl_intel_lp64_dll', 'mkl_intel_thread_dll']
library_dirs = ['C:\\Users\\vagrant\\src\\master-env\\libs']
define_macros = [('SCIPY_MKL_H', None)]
include_dirs = ['C:\\Users\\vagrant\\src\\master-env\\include']
mkl_info:
libraries = ['mkl_core_dll', 'mkl_intel_lp64_dll', 'mkl_intel_thread_dll']
library_dirs = ['C:\\Users\\vagrant\\src\\master-env\\libs']
define_macros = [('SCIPY_MKL_H', None)]
include_dirs = ['C:\\Users\\vagrant\\src\\master-env\\include']
最佳答案
lambertw 代码中有一个迭代。显然,当给出一个大的参数时,它不会收敛。 (正如 @unutbu 的回答所示,它是否收敛似乎取决于您的配置。)
这是一个适用于最大浮点值的(标量)正实参的替代方案:
import numpy as np
from scipy.optimize import fsolve
def lw(x):
"""Lambert W function, for real x >= 0."""
def func(w, x):
return np.log(x) - np.log(w) - w
if x == 0:
return 0
if x > 2.5:
lnx = np.log(x)
w0 = lnx - np.log(lnx)
elif x > 0.25:
w0 = 0.8 * np.log(x + 1)
else:
w0 = x * (1.0 - x)
return fsolve(func, w0, args=(x,))[0]
例如:
In [79]: lw(8.21016005323e+158)
Out[79]: 360.02763631519991
In [80]: np.finfo(1.0).max
Out[80]: 1.7976931348623157e+308
In [81]: lw(np.finfo(1.0).max)
Out[81]: 703.22703310477016
这是我的配置:
In [87]: scipy.show_config()
atlas_threads_info:
NOT AVAILABLE
blas_opt_info:
extra_link_args = ['-Wl,-framework', '-Wl,Accelerate']
extra_compile_args = ['-msse3', '-I/System/Library/Frameworks/vecLib.framework/Headers']
define_macros = [('NO_ATLAS_INFO', 3)]
atlas_blas_threads_info:
NOT AVAILABLE
openblas_info:
NOT AVAILABLE
lapack_opt_info:
extra_link_args = ['-Wl,-framework', '-Wl,Accelerate']
extra_compile_args = ['-msse3']
define_macros = [('NO_ATLAS_INFO', 3)]
atlas_info:
NOT AVAILABLE
lapack_mkl_info:
NOT AVAILABLE
blas_mkl_info:
NOT AVAILABLE
atlas_blas_info:
NOT AVAILABLE
mkl_info:
NOT AVAILABLE
关于python - 在 Python 中使用兰伯特函数时的 NaN 值 - 在 Enthought Canopy 中,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/23593267/