How do I make an array of complex numbers in Python?
In C++ STL we can write the following code:
class Complex {
public:
int re,
im;
float getModule() {
return sqrt(re * re + im * im);
}
};
vector< Complex > vec;
but in Python?
Python has built-in support for complex numbers. You can just enter them like that:
>>> a = 2 + 3j # or: complex(2,3)
>>> a
(2+3j)
>>> type(a)
<type 'complex'>
>>> a.real
2.0
>>> a.imag
3.0
>>>
As for the container, in Python you can start with a list:
>>> complex_nums_list = [2+3j, 3+4j, 4+5j]
>>> complex_nums_list
[(2+3j), (3+4j), (4+5j)]
Or you can use numpy.array, which would be more suited for numerical applications.
Extremely simple:
Python's has both a native list and a native complex type, so:
c = complex(real,imag)
or just
c = 1 + 2j
does the trick of creating one;
complexes = [ complex(i, i) for i in range(100) ]
creates thousand complex values in a list complexes.
You might want to have a look at numpy:
import numpy
arr = numpy.ndarray(1000, dtype=numpy.complex128)
You just create the list of values:
vec = [1+2j, 3+4j]
You can use the built-in complex class.
Or just use a complex literal: Python uses j for the imaginary unit.
z = complex(3, 4)
print(z, z.real, z.imag)
z = 3 + 4j
print(z)
output
(3+4j) 3.0 4.0
(3+4j)
The complex constructor also takes keyword arguments, so you can do
z = complex(real=3, imag=4)
with the args in either order. And that also means that you can even pass the args in a dict, if you want:
d = {'real': 3, 'imag': 4}
z = complex(**d)
There's also a built-in cmath module for mathematical functions of complex arguments.
A pure Python approach:
array_size = 10
vec = [complex()] * array_size
This will create a list of 10 empty complex numbers.
You can then set the first and second elements, if you want,
vec[0] = complex(2. , 2.,) # complex number 2+2j
vec[1] = 2 + 2j
or append a new element to your list:
vec.append(3 + 3j)
Actually, I want to sort numbers complex according to their module. This is my turn.
import math
class Complex:
def __init__( self, a, b ):
self.a = a
self.b = b
def getModule( self ):
return math.sqrt( self.a**2 + self.b**2 )
def __str__( self ):
''' Returns complex number as a string '''
return '(%s + i %s)' % (self.a, self.b)
def add(self, x, y):
return Complex(self.a + x, self.b + y)
def sub(self, x, y):
return Complex(self.a - x, self.b - y)
#input = [[2, 7],[5, 4],[9, 2],[9, 3],[7, 8], [2, 2], [1, 1]]
# Read the input from a given file complex.in,
# in fact is a matrix with Nx2 dimensions
# first line re1 im1
# second line re2 im2
# ...
#Example complex.in
#5
#2 7
#5 4
#9 2
#9 3
#7 8
f = open('complex.in','r')
input = [map(int, line.split(' ')) for line in f]
del input[0]
num = len( input )
complexes = [ Complex( i[ 0 ], i[ 1 ] ) for i in input ]
def swapp(c, a, b):
c[ a ], c[ b ] = c[ b ], c[ a ]
def sort( c ):
swapped = 1
for i in range(num - 1, 0, -1):
swapped = 1
for j in range(0, i):
if c[ j ].getModule() > c[ j + 1 ].getModule():
swapped = 0
swapp(c, j, j + 1)
if swapped:
break
sort( complexes )
f = open('complex.out','w')
for c in complexes:
f.write('%s\n' % c)
print c
list_of_complexes = [1+2j, 2, -10+0.5j]; sorted_list = sorted(list_of_complexes, cmp=abs)
[1+2j]. Or do you mean anarray.array?