Preallocation with object structures

2 次查看（过去 30 天）
Diego Hens
Diego Hens 2020-9-3
评论： J. Alex Lee 2020-9-4
Hello,
I have a question about preallocation with object-oriented programming.
I have this object:
This is the result of a few loops. I could have one only loop, but I prefere to do it step by step to better control that I'm not wasting my time with dumb errors. I think it's not important, but I'll show an example.
This is an object containing the tooth 11 (FDI nomenclature) of six different samples (STL-files) of teeth.
First I rotate and translate a tooth to fit a reference tooth (in this case tooth in second row). For this I get tform (transformation matrix) and movingReg (new set of points/vertices).
Then I do a nearest point analysis and get k and dist an calculate Fk which is the distance vector with which I calculate the MeanVertices for the reference tooth (that's why there is only one matrix, in the second row).
Matlab tells me to preallocate the whole time, which I don't know how to do with this object. How can I preallocate (for example) FDINumber11.Vertices (see the code bellow this paragraph) before reading the data and not knowing how many points the file has? I think solution would apply to the other characteristics.
for i=1:m % m is the amount of teeth, which is defined at the beginning
FDINumber11_STL = stlread(FDINumber11(i).STLPath);
FDINumber11(i).Vertices= FDINumber11_STL.Points;
FDINumber11(i).Faces = FDINumber11_STL.ConnectivityList;
end
The whole process takes a little while, not too much but I hope to one day try it with many more teeth, so optimization would be a good thing to do. The worst case is that I learn a good programming practice, so even in case I cannot preallocate here, I would be glad to get a good explanation of it.
As always thank you very much.
Diego
PS: I have an example of a preallocation here, used in this code and it seems to work.
summe1 = 0.0;
for i=1:m
summe1 = summe1 + (FDINumber11(i).Fk - FDINumber11(r).Vertices)/(m-1);
end

请先登录，再回答此问题。

采纳的回答

J. Alex Lee
J. Alex Lee 2020-9-3
I don't think you are understanding "preallocation" correctly based on your last example...matlab is [probably] asking you to "reserve space fo the m different stl files you want to process". In this case, m=6 if I understand your description. There is a simple fix:
for i = m:-1:1
FDINumber11_STL = stlread(FDINumber11(i).STLPath);
FDINumber11(i).Vertices= FDINumber11_STL.Points;
FDINumber11(i).Faces = FDINumber11_STL.ConnectivityList;
end
What this does is instead of go i = 1,2,3,4,5,6 it will go i = 6,5,4,3,2,1. This matters because
clear % clear all variables
x(6) = 1
is a way to implicitly tell matlab to preallocate 6 elements to the 1-D array x before assigning the 6th element. It works for structure arrays too.
It's also likely that you want to enapsulate all the analysis you do on an individual stl file into a single function, rather than do things in a loop with indices.
function results = stlAnalysis(stlpath)
% do stuff
end
  6 个评论
显示 4更早的评论
Diego Hens
Diego Hens 2020-9-4
Yes, that I have understood. When I replaced my code with a function I did not get the warning. I was just asking about the general use of preallocation. So, when I want to do a preallocation, I need to know the size of the matrix, right? In this case there is no preallocation, just the order of the loop.

请先登录，再进行评论。

更多回答（0 个）

类别

在 Help Center 和 File Exchange 中查找有关 Whos 的更多信息

标签

Community Treasure Hunt

Find the treasures in MATLAB Central and discover how the community can help you!

Start Hunting!

Translated by