python - 我在将 MATLAB 代码转换为 Python 时遇到问题
问题描述
我需要将下面显示的代码块转换为 Python。u
我创建了两个分别命名和命名的数组v
,并将它们放在 0 到 M-1 范围内的 for 循环中,我知道它的find
工作原理类似于 if 条件。我有一个问题,因为两者idx
都是u
数组。
MATLAB代码是这样的:
u = 0:(M-1);
v = 0:(N-1);
idx = find(u > M/2);
u(idx) = u(idx) - M; #I have a problem here
idy = find(v > N/2);
v(idy) = v(idy) - N;
基本上我在 Python 中所做的直到我遇到这个有问题的行是:
input_image = Image.open('./....image....')
input_image=np.array(input_image)
M,N = input_image.shape[0],input_image.shape[1]
FT_img = fftpack.fftshift(fftpack.fft2(input_image))
# Assign the order value
n = 2; # one can change this value accordingly
# Assign Cut-off Frequency
D0 = 60; # one can change this value accordingly
# Designing filter
u=[]
v=[]
for i in range(M-1):
u.append(i)
for i in range(N-1):
v.append(i)
解决方案
u = 0:(M-1)
在Matlab中做了什么,我们如何在Python中做同样的事情?
以下是您原始Matlab代码的摘录:
% BEGIN MATLAB %
u = 0:(M-1);
% END MATLAB %
代码有什么作用?
假设M = 7
. 然后Matlab代码简化:
u = 0:6;
结果是一个u
开始0
和结束于的数组6
:
u = [0 1 2 3 4 5 6]
本质上,您正在初始化一个连续整数数组。
在Python中有多种方法可以完成类似的事情:
# Begin Python
M = 7
u = list(range(0, M))
# End python
注意range(0, 7)
看起来像[0, ..., 5, 6]
,不是[0, ..., 6, 7]
Python 的函数自动从上限range
中减去1
如果你真的在做Matlab类型的东西,那么numpy
你想在Python中使用的库是:
import numpy as np
u = np.array(range(0, 7))
从0开始索引与从1开始索引
请注意,Matlab索引从 开始1
。
Python索引从0
.
ARRAY = ["red", "blue", "white", "green"]
+--------------+-------+--------+---------+---------+
| ARRAY | "red" | "blue" | "white" | "green" |
+--------------+-------+--------+---------+---------+
| PYTHON INDEX | 0 | 1 | 2 | 3 |
| MATLAB INDEX | 1 | 2 | 3 | 4 |
+--------------+-------+--------+---------+---------+
了解find
功能
find
从Matlab翻译成英文
考虑Matlabfind
中的函数:
idx = find(u > M/2); % this is matlab-code
函数调用find(u)
将在整个数组中搜索u
任何严格大于M/2
. find(u)
然后将返回大于的所有索引列表M/2
考虑以下find
函数示例:
u = [98 00 00 87 49 50 51 00 85];
% 1 2 3 4 5 6 7 8 9 .....ARRAY INDICIES
idx = find(u > 50);
disp(idx)
% displays .... 1 4 7 9
find(u > 50)
将找到u
大于或等于的每个元素的索引51
考虑代码u(idx) = 22;
我们有以下结果:
+---------------------+------+-----+-----+------+-----+-----+------+-----+------+
| MATLAB INDICIES | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 |
+---------------------+------+-----+-----+------+-----+-----+------+-----+------+
| print(u) | 99 | 00 | 00 | 99 | 49 | 50 | 51 | 00 | 99 |
+---------------------+------+-----+-----+------+-----+-----+------+-----+------+
| % u > 50? | %yes | %no | %no | %yes | %no | %no | %yes | %no | %yes |
+---------------------+------+-----+-----+------+-----+-----+------+-----+------+
| idx = find(u > 50); | | | | | | | | | |
| u(idx) = 22; | | | | | | | | | |
+---------------------+------+-----+-----+------+-----+-----+------+-----+------+
| print(u) | 22 | 0 | 0 | 22 | 49 | 50 | 22 | 0 | 22 |
+---------------------+------+-----+-----+------+-----+-----+------+-----+------+
数组中u
大于或等于的所有内容51
都替换为22
find
从英语翻译成Python
假设您u
在Python中有一个数组。
您想要替换每个大于或等于的整数51
,22
您可以使用以下库在Python中执行此操作:numpy
# This is Python (not matlab)
import numpy as np
u = [98 00 00 87 49 50 51 00 85];
u = np.array(u)
u[u > 50] = 22
# THIS IS PYTHON CODE (not matlab)
请注意,u[u > 50] = 22
这与以下内容相同:
# THIS IS PYTHON CODE (not matlab)
indicies = type(u).__gt__(u, 50)
u.__setitem__(indicies, 22)
# THIS IS PYTHON CODE (not matlab)
find
从Matlab转换为Python
如果您将部分原始代码从Matlab转换为Python,它将如下所示:
MATLAB输入:
M = 7
u = 0:(M-1);
idx = find(u > M/2);
u(idx) = u(idx) - M;
蟒蛇输出:
# THIS IS PYTHON CODE (not matlab)
import numpy as np
M = 7
u = np.array(range(0, M))
idx = u > M/2
u[idx] = u[idx] - M
# THIS IS PYTHON CODE (not matlab)
将所有Matlab代码翻译成英语和数学
在文章的开头,我解释了一些单独的Matlab代码的作用。
现在,让我们将整个Matlab脚本翻译成英语和数学。
*** 与您的原始/旧 MATLAB 相似的内容如下 ***
function u = GenerateArray(M)
u = 0:(M-1);
idx = find(u > M/2);
u(idx) = u(idx) - M;
end
M = 7;
u = GenerateArray(M);
N = 9;
v = GenerateArray(N);
*** 表格中的行为***
我认为Matlab代码作为表格比作为代码更容易理解:
+--------------+---------------------------+
| WHOLE NUMBER | ARRAY |
| `M` | `u` |
+--------------+---------------------------+
| 4 | 0 1 2 -1 |
| 5 | 0 1 2 -2 -1 |
| 6 | 0 1 2 3 -2 -1 |
| 7 | 0 1 2 3 -3 -2 -1 |
+--------------+---------------------------+
对于M > 7
:
- 数组的左半部分是:
[0, 1 , 2, 3, [...], floor(M/2)]
- 数组的右半部分是:
lang-none [(-1)*(x-0), (-1)*(x-1), (-1)*(x-2), [...], -3, -2, -1]
其中x等于floor((M-1)/2)
将所有Matlab代码翻译成Python
以下Python脚本与Matlab脚本具有相同的输出:
import numpy as np
import itertools as itts
def generate_data(array_size : int) -> type(np.array(range(0, 1))):
"""
+--------------+---------------------------+
| INPUT | OUTPUT |
+--------------+---------------------------+
| 4 | 0 1 2 -1 |
| 5 | 0 1 2 -2 -1 |
| 6 | 0 1 2 3 -2 -1 |
| 7 | 0 1 2 3 -3 -2 -1 |
+--------------+---------------------------+
* the left side of the array:
starts at:
zero
ends at:
floor(M/2)
counts by:
+1
looks like:
[0, 1 , 2, 3, [...], floor(M/2)]
* the right side of the array...
starts at
(-1) * floor((M-1)/2)
ends at:
-1
counts by:
-1
looks like:
[
(-1) * floor((M-1)/2),
(-1) * (floor((M-1)/2) - 1),
(-1) * (floor((M-1)/2) - 2),
[...],
-3,
-2,
-1
]
"""
# clean_input = int(dirty_input)
n = int(array_size)
# make the first element of the left side of the array be zero.
# left_side_first = 0
lsf = 0
# left_side_last = clean_input // 2
lsl = n // 2
# left_side_iterator = range(left_side_first, 1 + left_side_last)
lsit = range(lsf, 1 + lsl)
# `list` stands for "left side iterator"
right_side_first = (-1) * ((n - 1) // 2)
right_side_last = -1
right_side_iterator = range(right_side_first, 1 + right_side_last)
# merged_iterator = chain(left_side_iterator, right_side_iterator)
merged_iterator = itts.chain(lsit, right_side_iterator)
output = np.array(list(merged_iterator))
# We convert the iterator to a `list` because the following
# direct use of the iterator does not work:
#
# output = np.array(merged_iterator)
return output
我们可以像这样调用Python函数:
arr = generate_data(14)
print(arr)
输入的输出14
如下所示:
[ 0 1 2 3 4 5 6 7 -6 -5 -4 -3 -2 -1]
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