Loop generation doubt.
显示 更早的评论
Hi,
I need to create a loop. I have to do a numerical analysis of thousands of data points.
My equation is,
E=A*cos(k-(w*t))
I have A,k and w three of them have same length 1x10. In the case of t which i have 1x50.
what i have to do is i need to take the first value of A,k and w and vary t (means run with range of values) . I need to do the same processs for the rest of the rows of A,k and w and vary t.
To be more precise.
A k w T
1 1 1 1
2 2 2 2
3 3 3 3
4 4 4 4
N N N 5
6
N
the equation will be
First calculation need to be
E=1*cos(1-(1*(1....N)))
second
E=2*cos(2-(2*(1....N)))
.......
continue upto length of A,k,w
采纳的回答
the cyclist
2020-8-22
% DO NOT USE THESE. USE YOUR DATA. THESE ARE FOR AN EXAMPLE ONLY
T = rand(160547,1);
A = rand(44880,1);
k = rand(size(A));
w = rand(size(A));
%%%%%% Only use the code below %%%%%
% Preallocate memory for E
E = zeros(1,160547);
% Calculate E
for ii = 1:size(E2,2)
E(ii) = sum(A.*cos(k-(w.*T(ii))));
end
11 个评论
the cyclist
2020-8-22
FYI, if your data weren't so large (which you did not mention in your original question), then
E = sum(A.*cos(k-(w.*T')));
which is just the sum of my original answer, would give the same result.
This code work even though the vector T is a different size, because of the transpose and the implicit expansion I mentioned. It would calculate the 160547x44880 array, as you state. I suggest you try it on a smaller dataset
Your data are too big, so that huge intermediate array cannot be stored. But here is proof that on a smaller dataset, it gives the same result:
% DO NOT USE THESE. USE YOUR DATA. THESE ARE FOR AN EXAMPLE ONLY
T = rand(1605,1);
A = rand(44880,1);
k = rand(size(A));
w = rand(size(A));
% Preallocate memory for E
E = zeros(1,1605);
% Calculate E
for ii = 1:size(E,2)
E(ii) = sum(A.*cos(k-(w.*T(ii))));
end
% Calculate using implicit expansion instead
E2 = sum(A.*cos(k-(w.*T')));
% Show that the two results are equal
isequal(E,E2)
the cyclist
2020-8-22
编辑：the cyclist
2020-8-22
You can attach your data file here, using the INSERT icon that looks like a paperclip.
Martin Thomas
2020-8-22
Martin Thomas
2020-8-23
the cyclist
2020-8-23
编辑：the cyclist
2020-8-23
For my solutions above, it was important that your vectors were all row vectors, as you stated in your original question. In your actual code, they were not.
I believe the following aligns all the pieces correctly:
% Preallocate memory for eta
eta = zeros(160547,1);
% Precalculate K*X.
KX = K.*X;
% Calculate eta
for ii = 1:numel(eta)
eta(ii)=sum(amp'.*cos(KX-(f.*T_a(ii))));
end
The result I get is all NaNs, but I have not investigated why.
Martin Thomas
2020-8-23
the cyclist
2020-8-23
eta is always NaN because K has a NaN in it (so the sum is always NaN).
The first element of K is NaN because it comes from 1/f, and the first element of f is zero.
The first element of f is zero because you defined it that way:
f = (Fs/2*linspace(0,1,nfft/2+1)).*(2*pi);
So, you need to fix that in a way that makes sense for your application.
Martin Thomas
2020-8-23
Martin Thomas
2020-8-23
Martin Thomas
2020-8-23
the cyclist
2020-8-23
I don't really use fft. I would open a new question, and upload an image of the plot using INSERT again, along with the code that generates it.
Try to be very clear about your exact question.
更多回答（1 个）
the cyclist
2020-8-22
编辑：the cyclist
2020-8-22
You don't need to use a loop. MATLAB will do vectorized calculations.
If you have a fairly recent version of MATLAB, you can do this using implicit expansion of the vectors:
% Make up some data
A = rand(1,10);
k = rand(1,10);
w = rand(1,10);
t = rand(1,50);
% Calculate E
E = A.*cos(k-(w.*t'));
The output E will be 50x10.
Note that I took the transpose of t, and also used element-wise multiplication and not matrix multiplication. You can read about the difference here.
5 个评论
Martin Thomas
2020-8-22
Martin Thomas
2020-8-22
the cyclist
2020-8-22
The only code you need is the last line I wrote:
% Calculate E
E = A.*cos(k-(w.*t'));
The other lines of code are just making up some pretend input values, which I used to make sure that last line worked. You should just use your values for A, k, and w.
I didn't really understand your other comments, so if that doesn't help, maybe try to explain it again?
Martin Thomas
2020-8-22
Martin Thomas
2020-8-22
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