How do I extract data from MATLAB figures? (some error)

I want to extract 'y data' value from a fig file.

I input the following code in Matlab R2018b:

ezplot('y*(0.6326*log(y)+4.419*y + 30.48) - 80*sin(x)^2',[-5 5 -1 4])
>> h= gcf;
axObjs = h.Children
dataObjs = axObjs.Children
x = dataObjs(1).XData
y = dataObjs(1).YData

but I get the value for 'x axis' and 'y axis'. I don't need y axis. I only want to get the value of y date.

No matter what i do i can't make this to work. It's very strange. Any help will be greatly appreciated. Thanks in advance.

Answer 1

[Ameer Hamza]

ezplot() is being depreciated. Also, it generates a contour object, which is not so helpful to extract the data. Use fimplicit instead.

f = fimplicit(@(x, y) y.*(0.6326*log(y)+4.419*y + 30.48) - 80*sin(x).^2, [-5 5 -1 4]);
h= gcf;
axObjs = h.Children;
dataObjs = axObjs.Children;
x = dataObjs(1).XData;
y = dataObjs(1).YData;

[jaejin kim]

why didn't use dot log(y) and 4.419y but did sin(x). ??

I would appreciate it if you could explain why.

[Ameer Hamza]

But x is a vector, and therefore, sin(x) is a vector. But I don't want to do matrix multiplication. I want to do element-wise square; therefore, I specified .^ to let MATLAB know element-wise multiplication. For terms

0.6326*log(y)
4.419*y

It is a scalar multiplying with vector. You can use both * or .* There is no difference. I just skipped them for convenience.

Read here for more details: https://www.mathworks.com/help/matlab/matlab_prog/array-vs-matrix-operations.html

[jaejin kim]

It was really helpful!! Thanks for your help.

[Ameer Hamza]

I am glad to be of help!