问题描述
在numpy(或通常为python)中,我想利用Intel x86 FPU本机支持80位长的double数据类型这一事实。我怎样才能做到这一点。在我的机器上(Intel Core i7,macOS Catalina,python 3.8.1,numpy 1.19.1),以下尝试似乎失败了,因为似乎没有保留其他数字:
>>> scalar = np.array([1.4756563577476488347],dtype=np.float64)
... with np.printoptions(precision=100,suppress=False):
... print(scalar)
[1.475656357747649]
>>> scalar = np.array([1.4756563577476488347],dtype=np.float128)
... with np.printoptions(precision=100,suppress=False):
... print(scalar)
[1.4756563577476489169]
>>> scalar = np.array([1.4756563577476488347],dtype=np.longfloat)
... with np.printoptions(precision=100,suppress=False):
... print(scalar)
[1.4756563577476489169]
这似乎很奇怪,因为数据类型似乎就是我所认为的(64位与80位):
print(np.finfo(np.float64))
Machine parameters for float64
---------------------------------------------------------------
precision = 15 resolution = 1.0000000000000001e-15
machep = -52 eps = 2.2204460492503131e-16
negep = -53 epsneg = 1.1102230246251565e-16
minexp = -1022 tiny = 2.2250738585072014e-308
maxexp = 1024 max = 1.7976931348623157e+308
nexp = 11 min = -max
---------------------------------------------------------------
print(np.finfo(np.float128))
Machine parameters for float128
---------------------------------------------------------------
precision = 18 resolution = 1.0000000000000000715e-18
machep = -63 eps = 1.084202172485504434e-19
negep = -64 epsneg = 5.42101086242752217e-20
minexp = -16382 tiny = 3.3621031431120935063e-4932
maxexp = 16384 max = 1.189731495357231765e+4932
nexp = 15 min = -max
---------------------------------------------------------------
解析输入数字与它有什么关系吗?
解决方法
问题在于 Python 仅使用64位浮点,并且您正在将Python对象传递给np.array
。
尝试一下:
In [26]: scalar = np.array(['1.4756563577476488347'],dtype=np.float128)
In [27]: with np.printoptions(precision=100,suppress=False):
...: print(scalar)
...:
[1.4756563577476488347]
通过使用字符串作为文字,用于创建float128
对象的代码现在位于NumPy中,这将保留值的精度。