Trying to find values within a struct with a case

Hello,

I am working to extract the values of a 1x9 Struct (named FMtest) with 5 fields (named alpha, gamma, Fy, Fz, Mz). I need to find each measurement where alpha is 0 and then fit it to find further values (Cfa and Fy0 in my code

idx = find([FMtest(1:9).alpha] == 0);
pfy = polyfit(FMtest(1:9).alpha(idx),FMtest(1:9).Fy(idx),1);
Cfa = pfy(1)
Fy0 = pfy(2)

idx is returned as [53,156,259,361,463,565,667,769,871] which I am assuming corresponds to the array indicies where alpha is 0.

However, I am running into the following errors when trying to fit this case back on the struct

Errors:

Expected one output from a curly brace or dot indexing expression, but there were 9 results.

Error in RVD_Assignment4 (line 26)
pfy = polyfit(FMtest(1:9).alpha(idx),FMtest(1:9).Fy(idx),1);

Thank you,

Alex

Answer 1

[Ameer Hamza]

This indexing format is not correct according to MATLAB format. You should do something like this

x1 = [FMtest(1:9).alpha];
x2 = [FMtest(1:9).Fy];
idx = find(x1 == 0);
pfy = polyfit(x1(idx), x2(idx), 1);

[Alex Davison]

This worked, thank you!

[Ameer Hamza]

I am glad to be of help!