Converting MatLab for loop with array code to python

Question

I was given code in Matlab made by someone else and asked to convert to python. However, I do not know MatLab.This is the code:

for i = 1:nWind

[input(a:b,:), t(a:b,1)] = EulerMethod(A(:,:,:,i),S(:,:,i),B(:,i),n,scale(:,i),tf,options);

fprintf("%d\n",i);

for j = 1:b
        vwa = generate_wind([input(j,9);input(j,10)],A(:,:,:,i),S(:,:,i),B(:,i),n,scale(:,i));
        wxa(j) = vwa(1);
        wya(j) = vwa(2);
end


% Pick random indexes for filtered inputs
rand_index = randi(tf/0.01-1,1,filter_size);
inputf(c:d,:) = input(a+rand_index,:);
wxf(c:d,1) = wxa(1,a+rand_index);
wyf(c:d,1) = wya(1,a+rand_index);
wzf(c:d,1) = 0;

I am confused on what [input(a:b,:), t(a:b,1)] mean and if wxf, wzf, wyf are part of the MatLab library or if it's made. Also, EulerMethod and generate_wind are seprate classes. Can someone help me convert this code to python?

The only thing I really changed so far is changing the for loop from:

for i = 1:nWind

to

for i in range(1,nWind):

Answer 1

There's several things to unpack here.

First, MATLAB indexing is 1-based, while Python indexing is 0-based. So, your for i = 1:nWind from MATLAB should translate to for i in range(0,nWind) in Python (with the zero optional). For nWind = 5, MATLAB would produce 1,2,3,4,5 while Python range would produce 0,1,2,3,4.

Second, wxf, wyf, and wzf are local variables. MATLAB is unique in that you can assign into specific indices at the same time variables are declared. These lines are assigning the first rows of wxa and wya (since their first index is 1) into the first columns of wxf and wyf (since their second index is 1). MATLAB will also expand an array if you assign past its end.

Without seeing the rest of the code, I don't really know what c and d are doing. If c is initialized to 1 before the loop and there's something like c = d+1; later, then it would be that your variables wxf, wyf, and wzf are being initialized on the first iteration of the loop and expanded on later iterations. This is a common (if frowned upon) pattern in MATLAB. If this is the case, you'd replicate it in Python by initializing to an empty array before the loop and using the array's extend() method inside the loop (though I bet it's frowned upon in Python, as well). But really, we need you to edit your question to include a, b, c, and d if you want to be sure this is really the case.

Third, EulerMethod and generate_wind are functions, not classes. EulerMethod returns two outputs, which you'd probably replicate in Python by returning a tuple.

[input(a:b,:), t(a:b,1)] = EulerMethod(...); is assigning the two outputs of EulerMethod into specific ranges of input and t. Similar concepts as in points 1 and 2 apply here.

Those are the answers to what you expressed confusion about. Without sitting down and doing it myself, I don't have enough experience in Python to give more Python-specific recommendations.