Need help running simple equation over vector of data?
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Michael Ziedalski
on 1 Feb 2018
Commented: Star Strider
on 3 Feb 2018
So, I am new to Matlab and would appreciate all the help I can get. Recently, I coded an anonymous function (meant to represent a bivariate normal distribution) and was able to output a vector of results if I fed the x values to it (representing both of the means and st. deviations). This was my code
mu = [1;5]
sigma = [.5,0;0,.1]
data = mvnrnd(mu,sigma,100);
data1 = data(:,1);
data2 = data(:,2);
fun = @(x)(1/(2*pi*x(2)*x(4)*sqrt(1-.533^2)))*exp((-1/(2-2*.533^2))*((data1-x(1)).^2./(x(3)^2)+(data2-x(2)).^2./(x(4)^2)-(2*.533*(data1-x(1)).*(data2-x(2)))./(x(3)*x(4))))
fun([1,2,3,4]) %This outputs my answers.
The last line correctly gives me a 2x100 vector of results, since I gave 100 data values. But now I want to simplify this code b/c it was giving me issues elsewhere. I wanted to include data itself as a variable of sorts, and get the same answer. But only 1 answer gets outputted from the below code and that is puzzling.
fun = @(x, data)(1/(2*pi*x(2)*x(4)*sqrt(1-.533^2)))*exp((-1/(2-2*.533^2))*((data(1)-x(1)).^2./(x(3)^2)+(data(2)-x(2)).^2./(x(4)^2)-(2*.533*(data(1)-x(1)).*(data(2)-x(2)))./(x(3)*x(4))))
fun([1,2,3,4],[data])
ans =
0.0233
What am I missing here? Is the function somehow summing up all the values, or just calculating the result for the first row?
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Accepted Answer
Star Strider
on 1 Feb 2018
You are passing ‘data’ as a (100x2) matrix. You need to refer to the individual columns of ‘data’ in your function:
fun = @(x, data)(1/(2*pi*x(2)*x(4)*sqrt(1-.533^2)))*exp((-1/(2-2*.533^2))*((data(:,1)-x(1)).^2./(x(3)^2)+(data(:,2)-x(2)).^2./(x(4)^2)-(2*.533*(data(:,1)-x(1)).*(data(:,2)-x(2)))./(x(3)*x(4))));
That works correctly when I run it.
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