How to write a method to have input parameter a 1xN array?

I want to write a method (function) in my class to return a matrix containing pairs of (xyz) coordinates as output. The input has to be a 1xN array (a vector) containing angles. For example: 0:pi/50:2*pi . Please find below the method inside the Helix class I am talking about, as well as the entire Helix class if you may find it useful to understand what is happening (if not, scroll down to the method discussed above):

classdef Helix
    %Helix class
    %   Detailed explanation

properties(Access=protected)
        trk; %just a CdfTrack property for this class' objects
end

methods
        %constructor
        function obj = Helix(t)
            if nargin>0
                obj(numel(t))= Helix; %preallocate an array[vector] of the right size for (Helix-type) objects
                for i=1:numel(t)
                    obj(i).trk=t(i);  %for every vector's element, set its trk property accordingly
                end
            end    
        end

          %method to calculate the radius of the helix
          function r = radius(obj)
              r=zeros(numel(obj));
              for i=1:numel(obj)
                  h=obj(i).trk.curvature();
                  r(i)=1/(2*h);

              end
          end

          %method to calculate the center of the helix
          function position = center (obj)
            ll=numel(t);
            position=zeros(2,ll);  %an empty 2xnumel(t) matrix to be filled with (x,y) pairs
              for j=1:numel(t)
              wc = (r + obj(j).trk.d0()) * exp(i*(obj(j).trk.phi0()+ pi/2));%USELESS?
              x = (r + obj(j).trk.d0()) * cos(obj(j).trk.phi0());
              y = (-1)*(r+ obj(j).trk.d0()) * sin(obj(j).trk.phi0());
              position(1,j)=x; position(2,j)=y;
              end %here do we know about r from the previous function or do we have to call the radius() function INSIDE this second function?
          end

          %method to calculate the 3D coord. (x,y,z) from a vector of angles in radians
          function threed = points(obj,ve)     %does this function understands about obj?

              n=size(ve,2); %how many intermediate steps we have in the input range
              threed=zeros(n,3);%an empty nx3 matrix. we intend to transform it into: on rows pairs of (xyz) coordinates. n such pairs
            for j=1:numel(obj)
  %            w= wc- i*r*exp(i*(obj(j).trk.phi0()+q*time));

              for k=1:n    %we fill the above matrix with the coordinates as explained
              threed(k,1) = -(r(j) + obj(j).trk.d0())*sin(obj(j).trk.phi0()) + r(j) *sin(obj(j).trk.phi0()+ ve(1,k)); %this is x-coordinate.gradually go through (with that for loop) all the numbers in the (ve) vector to replicate the time evolution of coordinates
              threed(k,2)= (r(j) +obj(j).trk.d0())*cos(obj(j).trk.phi0()) - r(j) *cos(obj(j).trk.phi0()+ ve(1,k)); %this is y-coordinate at a given instant dictated by ve(1,k)
              threed(k,3) = obj(j).trk.z0() + abs(r)(j)*obj(1,k)*obj(j).trk.cotTheta();%this is z-coordinate at a given instant
              end

            end
          end
  end
  end

When working in the console and calling: h=Helix(t) ,where t is an object of CdfTrack type(with 5 properties) ---> puts in h an object of type helix, with a hidden property called trk (not very relevant to the question). Then v = h.points([0:pi/100:6*pi]) ---> error: Error using Helix/points Too many input arguments.

I tried to include this range of values inside a variable first and then to call the function using that variable. Nothing works.

What do I do wrong? Thank you!

[dpb]

The problem has to do with how the class methods are defined -- the function above would work passed a vector (altho it needs error checking to ensure it's a row or code to transform the input to the proper orientation for robustness that's not the actual problem).

The problem is the calling syntax isn't correct to call just a function; try just

v = points([0:pi/100:6*pi])

instead.

I've never used the Matlab class structure so don't know enough syntax to know just what is needed to make the function a method associated with a class, but there's where the issue is...

Answer 1

[Cedric]

Assuming that Helix is a handle class (subclass of handle), your method should be either static

 methods( Static = true )
     function threed = points( ve )
         ...
     end
 end

and called

 threed = Helix.points( ve ) ;

or it has to accept the object as first argument:

 function threed = points( obj, ve )
    ...

or

 function threed = points( ~, ve )
    ...

if your don't need the object (yet).

Your error message comes from the fact that the method is automatically/internally called with two arguments: the object and ve.

[Guillaume]

Well, the method clearly references object properties, so only option two is viable.

However, once that's fixed, it's likely that the next error will be:

undefined function of variable t

t might be meant to be obj instead.

Then, we have r that is undefined. Perhaps obj.r?

Note that the function provided would work with either handle or value class.

[Cedric]

Thank you Guillaume, I hadn't looked at the equations!

[Cedric]

Iustin, after you edited your code in the questions, I propose that you update the indentation and comment out faulty lines as follows:

 classdef Helix
    %Helix class
    %   Detailed explanation

    properties(Access=protected)
        trk; %just a CdfTrack property for this class' objects
    end

    methods
        %constructor
        function obj = Helix(t)
            if nargin>0
                obj(numel(t))= Helix; %preallocate an array[vector] of the right size for (Helix-type) objects
                for i=1:numel(t)
                   obj(i).trk=t(i);  %for every vector's element, set its trk property accordingly
                end
            end    
        end

        %method to calculate the radius of the helix
        function r = radius(obj)
            r=zeros(numel(obj));
            for i=1:numel(obj)
                h=obj(i).trk.curvature();
                r(i)=1/(2*h);
            end
        end

        %method to calculate the center of the helix
        function position = center(obj)
            ll=numel(t);
            position=zeros(2,ll);  %an empty 2xnumel(t) matrix to be filled with (x,y) pairs
            for j=1:numel(t)
                %%wc = (r + obj(j).trk.d0()) * exp(i*(obj(j).trk.phi0()+ pi/2));%USELESS?
                %%x = (r + obj(j).trk.d0()) * cos(obj(j).trk.phi0());
                %%y = (-1)*(r+ obj(j).trk.d0()) * sin(obj(j).trk.phi0());
                %%position(1,j)=x; position(2,j)=y;
            end %here do we know about r from the previous function or do we have to call the radius() function INSIDE this second function?
        end

        %method to calculate the 3D coord. (x,y,z) from a vector of angles in radians
        function threed = points(obj,ve)     %does this function understands about obj?
            n=size(ve,2); %how many intermediate steps we have in the input range
            threed=zeros(n,3);%an empty nx3 matrix. we intend to transform it into: on rows pairs of (xyz) coordinates. n such pairs
            for j=1:numel(obj)
                %            w= wc- i*r*exp(i*(obj(j).trk.phi0()+q*time));
                for k=1:n    %we fill the above matrix with the coordinates as explained
                    %%threed(k,1) = -(r(j) + obj(j).trk.d0())*sin(obj(j).trk.phi0()) + r(j) *sin(obj(j).trk.phi0()+ ve(1,k)); %this is x-coordinate.gradually go through (with that for loop) all the numbers in the (ve) vector to replicate the time evolution of coordinates
                    %%threed(k,2)= (r(j) +obj(j).trk.d0())*cos(obj(j).trk.phi0()) - r(j) *cos(obj(j).trk.phi0()+ ve(1,k)); %this is y-coordinate at a given instant dictated by ve(1,k)
                    %%threed(k,3) = obj(j).trk.z0() + abs(r)(j)*obj(1,k)*obj(j).trk.cotTheta();%this is z-coordinate at a given instant
                end
            end
        end

    end

 end

where I commented out 6 lines (starting with %%). After doing this, you can start playing with your Helix object(s):

 >> h = Helix(1:4)
 h = 
  1×4 Helix array with no properties.

 >> h(1).points( [1,2] )
 ans =
     0     0     0
     0     0     0

and see that it works except for the computations that had problems. In fact you get the value of threed defined during its initialization (0s). So the OOP mechanisms work, and you can focus on the rest.

One error was coming for your attempt to access the _j_th element of the output of ABS apparently (?)

 abs(r)(j)

which you cannot do in MATLAB. You have to store the output in an intermediary variable and then index the variable.