How to write this thetta fuction in Matlab? I have an example code in Python
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How to write this thetta fuction in Matlab?
Someone wrote it in Python like this:
def thetta(r):
thettar = np.zeros(r.size)
h = (r_2 - r_1) / N
for i in range(r.size):
for j in range(i):
thettar[i] += h * 0.5 * (1 / (r[j] * math.tan(betta(r[j]))) + 1 / (r[j+1] * math.tan(betta(r[j+1]))))
return thettar
10 个评论
Askic V
2023-1-26
Can you please show us your current attempt?
Beket
2023-1-26
Askic V
2023-1-26
How is betta defined? You should be able to execute the same code in Python and Matlab and compare results.
Matlab has some very good built in functions for integration. For numerical integration I use cumtrapz, but I guess your task is to rewrite the Python implementation to Matlab.
Beket
2023-1-26
Dyuman Joshi
2023-1-26
编辑：Dyuman Joshi
2023-1-26
Are you getting an error? If so, please mention the full error.
And/Or are you not getting the output you want? In that case, attach or provide the full code and data for r (a sample data would work as well) and the corresponding required output.
Beket
2023-1-26
Dyuman Joshi
2023-1-26
编辑：Dyuman Joshi
2023-1-26
What are c_rinf, w, s and z in the definition of betta?
Are they defined before their use in betta?
Beket
2023-1-26
Dyuman Joshi
2023-1-26
You can attach it here, use the paperclip icon.
Or you can copy paste releveant code.
Beket
2023-1-26
采纳的回答
Ok, without going into too much details, let's say you have the following Python functions that you need to rewrite in Matlab.
Python code:
import math
import numpy as np
def thetta(r, N):
thettar = np.zeros(r.size)
r_1 = r[0]
r_2 = r[-1]
h = (r_2 - r_1) / N
for i in range(r.size):
for j in range(i):
thettar[i] += h * 0.5 * (1 / (r[j] * math.tan(betta(r[j]))) + 1 / (r[j+1] * math.tan(betta(r[j+1]))))
return thettar
def betta(x):
return 2*x
% Test results
N = 10
r_1 = 1
r_2 = 5
h = h = (r_2 - r_1) / N
r = np.arange(r_1 ,r_2 +h,h)
y = thetta(r, N)
print(y)
The Python code will produce teh following result:
[ 0. -0.4933463 -0.66999674 -0.41547207 -0.42690584 -0.69679015
-0.82237975 -0.70521665 -0.7204894 -0.93958357 -1.06804844]
Now, the equivalent implementation in Matlab would be:
clear
clc
r_1 = 1;
r_2 = 5;
N = 10;
h = (r_2 - r_1) / N;
% betta = @(x) 2*x; you can use function handle instead of full function def
r = r_1:h:r_2; % to have the same number of elements compared to python
thettar = zeros(size(r));
for i = 1: size(r,2)-1
for j = 1:i
thettar(i+1) = thettar(i+1) + h * 0.5 * (1 / (r(j) * tan(betta(r(j)))) + 1 / (r(j+1) * tan(betta(r(j+1)))));
end
end
thettar
%Some simple betta function, just to be used for test
function y = betta(x)
y = 2*x;
end
and this code will produce the result:
thettar =
0 -0.4933 -0.6700 -0.4155 -0.4269 -0.6968
-0.8224 -0.7052 -0.7205 -0.9396 -1.0680
So, basically that is all you need. The biggest hassle is to keep in mind that index strats with 0 in Python and with 1 in Matlab.
5 个评论
Beket
2023-1-26
Beket
2023-1-26
Askic V
2023-1-26
First of all, all function definitions should go at the end of the script or to save each function in the separate file 'function_name.m' (name of the file must be the same as the name of the function inside it).
Second, you use undefined variables, for example: Q_rk, how Matlab would know in the line:
c_rinf = Q_rk / (2 * pi * r * b(r));
what Q_rk is?
Beket
2023-1-26
You did, but it is not a global variable, and it is not visible inside the function:
function c_rinf = c_rinf(r)
c_rinf = Q_rk / (2 * pi * r * b(r));
end
so you need to send it as an input argument, for example:
function c_rinf = c_rinf(Q_rk, r)
c_rinf = Q_rk / (2 * pi * r * b(r));
end
You need to pay attention to this type of things.
Next you use a lot of bad practice, for example, variable name is the same as function etc...
更多回答（1 个）
Dyuman Joshi
2023-1-26
@Beket, your code needs some changes
94th and 95th line of your code, you used b in c_rinf before defining it.
c_rinf = @(r) Q_rk ./ (2 .* pi .* r .* b(r));
b = @(r) b_1 - (b_1 - b_2) ./ (r_2 - r_1) .* (r - r_1);
Similarly, in lines 110th and 111th, you used r in thettar before defining it.
thettar = zeros(size(r));
r = linspace(r_1, r_2, N);
Correct the order and the error will be rectified.
Also, while defining a function handle, it's better to use element-wise operators .*, ./ and .^ , you can see that change above in c_rinf and b.
Your code still has some errors, mostly syntax errors (check line 121 and 150).
Additionally, what is the purpose of these lines?
bettar = betta(r);
thettar = thettar(r);
4 个评论
Beket
2023-1-26
Dyuman Joshi
2023-1-26
I already have your original code. Is this one different from that one?
Beket
2023-1-26
Dyuman Joshi
2023-1-26
Did you make the changes I suggested in my answer and run the code?
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