Multiplication of elements in array in for loop

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EraGum
EraGum 2020-4-5
评论： Srivardhan Gadila 2020-4-10
Hello,
I need an advice how can I shorten my code. I feel like it should be a very easy thing to do but can't think of anything.
For my code I am using three columns of data from excel spreadsheet, e.g. column A, E and G. Each column has 29 rows.
The code has a FOR loop, which determines the probability estimation. The line, which concerns me is:
prob(i)=normpdf(A1(i),mu(i),sigma(i))*normpdf(A2(i),mu(i),sigma(i))*normpdf(A3(i),mu(i),sigma(i))... *normpdf (A29(i), mu(i), sigma(i)) ;
Is there any way that could help me to shorten the whole line and do 29 multiplications automatically?
Could I write something like this?
prob(i)=prod(normpdf(A_data(i), mu(i), sigma(i)))
  2 个评论
David Hill
David Hill 2020-4-5
I don't understand. What is A1....A29 is that A(1:29)? What is mu and sigma? Are they E(1:29) and G(1:29)?
EraGum
EraGum 2020-4-6
Yes, A1 is A(1:29), A2 is A(2:29) and etc.
mu and sigma were calculated using the data from columns E and G.
e.g.
mu(i)=k(i)*(E_data(i)^x(i))*(G_data(i)^y(i));
k, x and y are "calibration parameters''.
In the question I tried to simplify my code so it wouldn't look too confusing.

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回答（1 个）

Srivardhan Gadila
编辑：Srivardhan Gadila 2020-4-10
Refer to arrayfun and use it as follows:
Let all the A1(i), A2(i) ... A29(i) be in the array AiArray
prob(i)=prod(arrayfun(@(Ai)normpdf(Ai, mu(i), sigma(i)),AiArray))
The following code might help you understand:
N = 5; %i=1:N
mu = randn(N,1);
sigma = abs(randn(N,1));
A1 = randn(N,1);
A2 = randn(N,1);
A3 = randn(N,1);
A1Array = [A1(1);A2(1);A3(1)];
A2Array = [A1(2);A2(2);A3(2)];
A3Array = [A1(3);A2(3);A3(3)];
A4Array = [A1(4);A2(4);A3(4)];
A5Array = [A1(5);A2(5);A3(5)];
% The above AiArray's are defined only to understand what I'm trying to explain
Amatrix = [A1 A2 A3];
prob = [];
for i=1:N
prob(i)=prod(arrayfun(@(Ai)normpdf(Ai, mu(i), sigma(i)),Amatrix(i,:)));
end
  2 个评论
EraGum
EraGum 2020-4-10
Thank you for reply. I used your advice and changed my code to:
AiArray=xlsread('NACA_data.xlsx',1,'A1:A29');
for i=1:length(AiArray)
prob(i)=prod(arrayfun(@(Ai)normpdf(Ai, mu(i), sigma(i)),AiArray));
end
However, I keep geeting prob as 0.
Did I understand you right?
Srivardhan Gadila
Srivardhan Gadila 2020-4-10
@EraGum, I have edited the answer and provided example code for clarity.

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