struct for multiple shapes with similar inputs

I am trying to create a struct that takes inputs for a shape (in this case theyre all rectangles) base, height, xbar and ybar of a shape and uses this information to fill in the rest of the vakues for the shape (Area, Ixx, Iyy, etc).

Id like to apply this struct to mulitple shapes

Then, also sum some of the values across the different shapes and store this in a seperate variable from the struct (Ixx_prime = (shape_1.Ixx + shape_2.Ixx + shape_3.Ixx)

This was my approach

% Set up  
shape = struct('base', [], 'height', [], 'Area', [], 'xbar', [], 'ybar', [], ...
    'Areax2', [], 'Areay2', [], 'Areaxy', [], 'Ixx', [], 'Iyy', [], 'Ixy', [])

shape = struct with fields:
      base: []
    height: []
      Area: []
      xbar: []
      ybar: []
    Areax2: []
    Areay2: []
    Areaxy: []
       Ixx: []
       Iyy: []
       Ixy: []

shape.base = 10; % 
shape.height = 50; %
shape.Area = shape.base*shape.height;
shape.xbar = -15; %
shape.ybar = 30; %
shape.Areax2 = shape.Area*(shape.xbar^2);
shape.Areay2 = shape.Area*(shape.ybar^2);
shape.Areaxy = shape.Area*shape.xbar*shape.ybar;
shape.Ixx = (shape.base*shape.height^3)/12;
shape.Iyy = (shape.base^3*shape.height)/12;
shape.Ixy = 0

shape = struct with fields:
      base: 10
    height: 50
      Area: 500
      xbar: -15
      ybar: 30
    Areax2: 112500
    Areay2: 450000
    Areaxy: -225000
       Ixx: 1.0417e+05
       Iyy: 4.1667e+03
       Ixy: 0

shapeA = shape

shapeA = struct with fields:
      base: 10
    height: 50
      Area: 500
      xbar: -15
      ybar: 30
    Areax2: 112500
    Areay2: 450000
    Areaxy: -225000
       Ixx: 1.0417e+05
       Iyy: 4.1667e+03
       Ixy: 0

shapeA.base = 50; % 
shapeA.height = 10; %
shapeA.xbar = 0; %
shapeA.ybar = 0 %

shapeA = struct with fields:
      base: 50
    height: 10
      Area: 500
      xbar: 0
      ybar: 0
    Areax2: 112500
    Areay2: 450000
    Areaxy: -225000
       Ixx: 1.0417e+05
       Iyy: 4.1667e+03
       Ixy: 0

This does not refill the subsequent values for the new shape.

Any ideas for a better approach? I've been looking into classes https://au.mathworks.com/help/matlab/matlab_oop/example-representing-structured-data.html but am unsure how to approach.

Cheers for any advice!

Answer 1

[Benjamin Kraus]

There are options for doing this without using classes, but I think classes is probably what you want to do.

I'm not sure I follow what xbar and ybar mean, but let me give an example of a class with just height, base, area and circumference, and you can extrapolate from there.

classdef Shape
    properties
        Height
        Base
    end
    properties (Dependent)
        % These properties are derived from other properties. By tagging
        % them as "Dependent" you indicate that the value of these
        % properties depends on the value of other properties.
        Area
        Circumference
    end
    methods
        function a = get.Area(obj)
            % This function will execute whenever you attempt to query the
            % value of the "Area" property.
            a = obj.Height*obj.Base;
        end
        function c = get.Circumference(obj)
            % This function will execute whenever you attempt to query the
            % value of the "Circumference" property.
            c = 2*(obj.Height+obj.Base);
        end
    end
end

Once you've written that object, you can create a Shape object and then set the Height and Base, and MATLAB will calculate the Area and Circumference.

s = Shape;
s.Height = 10;
s.Base = 5;
disp(s)

The output will look like this:

s = 

  Shape with properties:

           Height: 10
             Base: 5
             Area: 50
    Circumference: 30

[Samantha May]

This is a great step in the right direction. Thank you for the example.

[Samantha May]

Classes are definetely the way to go!

As I cannot use classes in Live Editor, I have opted to make a class file and reference it. Works flawlessly. This allows me to Sum values across multiple objects of the class Shape!

Absolutely stoked. Thank you

[Benjamin Kraus]

I'm glad you were able to get things up and running. Welcome to the world of Object Oriented Programming (OOP) in MATLAB.

I wish there was a way to define a MATLAB class in-line (both in the Live Editor and in other places), but as you said, that is not currently possible.