# NumPy - 数学函数

## 三角函数

NumPy具有标准三角函数，该函数返回给定角度的弧度的三角比例。

import numpy as np
a = np.array([0,30,45,60,90])

print 'Sine of different angles:'
#通过乘以 pi/180 转换为弧度
print np.sin(a*np.pi/180)
print '\n'

print 'Cosine values for angles in array:'
print np.cos(a*np.pi/180)
print '\n'

print 'Tangent values for given angles:'
print np.tan(a*np.pi/180)

Sine of different angles:
[ 0.          0.5         0.70710678  0.8660254   1.        ]

Cosine values for angles in array:
[  1.00000000e+00   8.66025404e-01   7.07106781e-01   5.00000000e-01
6.12323400e-17]

Tangent values for given angles:
[  0.00000000e+00   5.77350269e-01   1.00000000e+00   1.73205081e+00
1.63312394e+16]

arcsinarcos，和 arctan 函数返回给定角度的sincostan的三角逆，这些函数的输出可以通过 numpy.degrees()函数将弧度转换为度来验证。

import numpy as np
a = np.array([0,30,45,60,90])

print 'Array containing sine values:'
sin = np.sin(a*np.pi/180)
print sin
print '\n'

print 'Compute sine inverse of angles. Returned values are in radians.'
inv = np.arcsin(sin)
print inv
print '\n'

print 'Check result by converting to degrees:'
print np.degrees(inv)
print '\n'

print 'arccos and arctan functions behave similarly:'
cos = np.cos(a*np.pi/180)
print cos
print '\n'

print 'Inverse of cos:'
inv = np.arccos(cos)
print inv
print '\n'

print 'In degrees:'
print np.degrees(inv)
print '\n'

print 'Tan function:'
tan = np.tan(a*np.pi/180)
print tan
print '\n'

print 'Inverse of tan:'
inv = np.arctan(tan)
print inv
print '\n'

print 'In degrees:'
print np.degrees(inv)

Array containing sine values:
[ 0.          0.5         0.70710678  0.8660254   1.        ]

Compute sine inverse of angles. Returned values are in radians.
[ 0.          0.52359878  0.78539816  1.04719755  1.57079633]

Check result by converting to degrees:
[  0.  30.  45.  60.  90.]

arccos and arctan functions behave similarly:
[  1.00000000e+00   8.66025404e-01   7.07106781e-01   5.00000000e-01
6.12323400e-17]

Inverse of cos:
[ 0.          0.52359878  0.78539816  1.04719755  1.57079633]

In degrees:
[  0.  30.  45.  60.  90.]

Tan function:
[  0.00000000e+00   5.77350269e-01   1.00000000e+00   1.73205081e+00
1.63312394e+16]

Inverse of tan:
[ 0.          0.52359878  0.78539816  1.04719755  1.57079633]

In degrees:
[  0.  30.  45.  60.  90.]

## numpy.around()

numpy.around(a,decimals)
Sr.No.Parameter & Remark
1

a

2

decimals

import numpy as np
a = np.array([1.0,5.55, 123, 0.567, 25.532])

print 'Original array:'
print a
print '\n'

print 'After rounding:'
print np.around(a)
print np.around(a, decimals = 1)
print np.around(a, decimals = -1)

Original array:
[   1.       5.55   123.       0.567   25.532]

After rounding:
[   1.    6.   123.    1.   26. ]
[   1.    5.6  123.    0.6  25.5]
[   0.    10.  120.    0.   30. ]

## numpy.floor()

import numpy as np
a = np.array([-1.7, 1.5, -0.2, 0.6, 10])

print 'The given array:'
print a
print '\n'

print 'The modified array:'
print np.floor(a)

The given array:
[ -1.7   1.5  -0.2   0.6  10. ]

The modified array:
[ -2.   1.  -1.   0.  10.]

## numpy.ceil()

ceil()函数返回输入值的上限，即标量x的ceil是最小的整数i，使得i>=x。

import numpy as np
a = np.array([-1.7, 1.5, -0.2, 0.6, 10])

print 'The given array:'
print a
print '\n'

print 'The modified array:'
print np.ceil(a)

The given array:
[ -1.7   1.5  -0.2   0.6  10. ]

The modified array:
[ -1.   2.  -0.   1.  10.]

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