Subscript indices must either be real positive integers or logicals.

Im trying to create a mario game and am coming across the error mentioned above on this line:

if  (handles.Template(Row,Column) == 0);

The rest of the code is shown below:

[Rows Columns Color] = size(handles.Template)
 for RowIndex = 1:1:Rows
     for ColumnIndex = 1:1:Columns
         if handles.Template(RowIndex, ColumnIndex, 2) <= 22 &&...
           handles.Template(RowIndex, ColumnIndex, 3) <= 24
             handles.Template(RowIndex,ColumnIndex,:) == 1;
         else
            handles.Template(RowIndex,ColumnIndex,:) == 0;     
         end
     end
 end

   configurePin(a,'A0','AnalogInput')
        CurrentX = 0;
   for time = [1:1:10000];
       A2Voltage = readVoltage(a, 'A0');
  if A2Voltage >= 3
   Row = floor(handles.SpriteAxis.Position(2)/29);
   Column = floor((handles.SpriteAxis.Position(1)+15)/29);
     set(handles.SpriteAxis,'xdir','normal')
  set(M,'visible','off');
  set(A,'visible','on');
  set(R,'visible','off');
  set(I,'visible','off');
  axis off
   pause(.04)
  set(M,'visible','off');
  set(A,'visible','off');
  set(R,'visible','on');
  set(I,'visible','off');
   axis off
   pause(.04)
  set(M,'visible','off');
  set(A,'visible','on');
  set(R,'visible','off');
  set(I,'visible','off');
   axis off
   pause(.04)
   set(M,'visible','off');
  set(A,'visible','off');
  set(R,'visible','off');
  set(I,'visible','on');
   axis off
    if  (handles.Template(Row,Column) == 0);
      handles.SpriteAxis.Position(1) = handles.SpriteAxis.Position(1)+15;
    end  
  elseif A2Voltage < 2
  Row = floor(handles.SpriteAxis.Position(2)/29);
  Column = floor((handles.SpriteAxis.Position(1)-15)/29);
  set(handles.SpriteAxis,'xdir','reverse')
  set(M,'visible','off');
  set(A,'visible','on');
  set(R,'visible','off');
  set(I,'visible','off');
  axis off
   pause(.04)
  set(M,'visible','off');
  set(A,'visible','off');
  set(R,'visible','on');
  set(I,'visible','off');
   axis off
   pause(.04)
  set(M,'visible','off');
  set(A,'visible','on');
  set(R,'visible','off');
  set(I,'visible','off');
   axis off
   pause(.04)
   set(M,'visible','off');
  set(A,'visible','off');
  set(R,'visible','off');
  set(I,'visible','on');
   axis off
    if  (handles.Template(Row,Column) == 0)
        handles.SpriteAxis.Position(1) = handles.SpriteAxis.Position(1)-15;
    end
  end
   end

Answer 1

[Jan]

What is your question?

You have to use the debugger to find the reason of the problem. The indices are defined here:

Row = floor(handles.SpriteAxis.Position(2)/29);
Column = floor((handles.SpriteAxis.Position(1)+15)/29);

Obviously at least one of them is not positive. You can test this easily by letting Matlab stop at the error:

dbstop if error

or use the corresponding menu in the editor. Then run the code again until it stops at the error. Now check the values of Row and Column.

Note: See http://www.mathworks.com/matlabcentral/answers/35676-why-not-use-square-brackets for modifying:

for time = [1:1:10000];

to the faster and nicer

for time = 1:10000

[Curtis Vannor]

when I removed the floor on both the row and column the value for row was 0.7920 and the value for column was 0.6483 and I am still getting the same error

[Stephen23]

@Curtis Vannor: MATLAB indices start from one, as this is the norm in mathematics. This is explained in the introductory tutorials:

https://www.mathworks.com/help/matlab/getting-started-with-matlab.html

Note that floor(0.7920) is zero, which is less than one.

[Curtis Vannor]

Ok thanks. I changed the row and column to this:

if true
Row = handles.SpriteAxis.Position(2)+1;
Column = (handles.SpriteAxis.Position(1)+1);
end

which gives me 4.8 for column and 23.9692 for row. However I am still getting the same error at this line:

if true
if  (handles.Template(Row,Column) == 0);
  handles.SpriteAxis.Position(1) = handles.SpriteAxis.Position(1)+1;
end  
end

Is there something I am missing?

[Jan]

@Curtis: The error message is clear: Indices must be positive integers. Neither 0, nor 4.8 are valid integers. I guess you want ceil.

[Curtis Vannor]

Ok I understand. But I am curious if there is a way to check the color of the template axis in the area in front of mario before mario approaches that are in order to dictate whether or not mario can interact with that area. The stage is as shown:

And the template under this is as shown:

The solid objects are shown in blue and green on the template but they are kind of difficult to see. Can you help me with this? I used ceil but i think since the template has smaller dimensions (15x212) than the stage im getting a subscript indices exceed matrix dimensions error.

[Jan]

@Curtis: To asnwer this question it is required to understand how the data a represented in your code. The current description is vague only. I can only guess, why you divide "handles.SpriteAxis.Position(2)" by 29.

You got some advices how to create the correct indices (positive integers), but did not explain, if you have considered them and if the code runs with success now.

I recommend, that you concentrate on the actual question: Post only the relevant code, omit the screenshots. Perhaps you need something like this:

 I have 2 matrices, one with dimension AxB, and one with MxN.
 Assuming that the both cover the same area, how can I get the
 indices of elements belonging together? I've tried it with
 this code: [...], but the resulting indices are [wrong/bad/0].

[Curtis Vannor]

I apoligize. I have two matrices, one with dimensions 227x3392x3, which is the stage, and the other with dimensions of 15x212x3, which is the template. Both cover the same area. How can I index an area on the stage that is common for both matrices? I attempted set discreet values to the areas of the template matrix that were colored using the code below:

[Rows Columns Color] = size(handles.Template)
 for RowIndex = 1:1:Rows
     for ColumnIndex = 1:1:Columns
         if handles.Template(RowIndex, ColumnIndex, 2) <= 22 &&...
           handles.Template(RowIndex, ColumnIndex, 3) <= 24
             handles.Template(RowIndex,ColumnIndex,:) == 1;
         else
            handles.Template(RowIndex,ColumnIndex,:) == 0;     
         end
   end
end

And I tried to reference a certain area of the template relative to mario's position with the following code:

Row = ceil((handles.SpriteAxis.Position(2)+1)/29);
Column = ceil((handles.SpriteAxis.Position(1)+1)/29);

and

   if  (handles.Template(Row,Column) == 0);
      handles.SpriteAxis.Position(1) = handles.SpriteAxis.Position(1)+1;
    end

with 29 being the width and height of the mario sprite. This resulted in the values for both row and column being one, not changing as mario moves into a pipe, therefore allowing mario to walk through it.

I also tried:

Row = ceil((handles.SpriteAxis.Position(2)+1));
Column = ceil((handles.SpriteAxis.Position(1)+1);

this resulted in indices of 24 and 5, which exceeds the dimensions of the template matrix.

[Walter Roberson]

The conversion ratio is 16, not 29.

Instead of hardcoding the 29 or whatever everywhere, you should write a couple of small functions that convert between coordinate systems.

At any one point, you have a Mario position, which needs to be defined by reference to a point and to a distance left and right and up and down relative to the point (and perhaps more detailed than that, if for example it matters exactly where Mario's hand is, not just whether the Mario sprite overlaps the rope.) You also have a Mario velocity, which needs to have horizontal and vertical components and be signed quantities.

And a fundamental query you need to make against the template is "Given the position parameters and the velocity components, is there anything that would be interacted with within (velocity times timestep) distance ? Because if there isn't then you just move and go on to the next time step; if there is something in reach then you have to make a decision about what to do. You should not be asking "is Mario closer than this fixed value to something to interact with" because Mario does not have a constant velocity.

So you need a routine that not only converts Mario's position to template coordinates but also converts Mario's velocity to template relative coordinates. And then extracts that portion of the template and makes a decision.

You might potentially end up using variable time step: for example if Mario is about to hit something that is 3 pixels away when traveling at 20 pixels per timestep, then the result is going to be different than if the same object as 17 pixels away when traveling at 20 pixels per timestep.

Also you might need to take acceleration into account -- if, that is, you model jumping with regards to gravity rather than some kind of linear process.

[Curtis Vannor]

How would I set the reference point?

[Walter Roberson]

If there are no "hot spots" on the sprites (places that should act differently -- e.g., does it matter whether it is Mario's foot that touches the rope compared to Mario's hand?) then it is easiest to use the centroid of the sprite as the reference point, as then the distance left and right would be the same. This does have a small challenge if the sprite is an odd number of pixels in width: you should be conscious of whether the reference point is the center of the pixel or the left edge or the right edge of the pixel.

[Curtis Vannor]

Im not really sure what you mean by converting between the coordinate systems. I made this function:

function [ new_coordinates ] = coortrans( in1,in2 )
%UNTITLED2 Summary of this function goes here
%   Detailed explanation goes here
size(in1)/size(in2)
end

Which gave a ratio of the size of the larger stage to the template, but what do I do from here?

Also, will the centroid be necessary since the sprite is its own axis? Couldn't I just use the position parameter of the axis itself?