Error : Indices must either be real positive integers or logicals.

when I change number of nodes from 4 to 8 I get this

Error: Subscript indices must either be real positive integers or logicals.
                                                                 Error in RectangularPlate22 (line 63)
                                                                  X(:,iel) = coordinates(nodes(iel,:),1) ;_|

How could i resolvethis error and make it working for 8 nodes per element???

% Variable Description:
%           L - Length of the Plate along X-axes
%           B - Breadth of the Plate along Y-axes
%           Nx - Number of Elements along X-axes
%           Ny - Number of Elements along Y-axes
%           coordinates - The nodal coordinates of the mesh
%           -----> coordinates = [node X Y] 
%           nodes - The nodal connectivity of the elements
%           -----> nodes = [node1 node2......]    
%--------------------------------------------------------------------------
clc ; clear all ;
% Variables which can be changed
% Dimensions of the plate
L = 0.5 ;             % Length of the Plate along X-axes
B = 0.5 ;             % Breadth of the Plate along Y-axes
% Number of Elements required 
Nx = 20 ;            % Number of Elements along X-axes
Ny = 20 ;            % Number of Elements along Y-axes
%----------------------------------------
% From here dont change
nel = Nx*Ny ;        % Total Number of Elements in the Mesh
nnel = 8 ;           % Number of nodes per Element
% Number of points on the Length and Breadth
npx = Nx+1 ;
npy = Ny+1 ;
nnode = npx*npy ;      % Total Number of Nodes in the Mesh
% Discretizing the Length and Breadth of the plate
nx = linspace(0,L,npx) ;
ny = linspace(0,B,npy) ;
[xx, yy] = meshgrid(nx,ny) ;
% To get the Nodal Connectivity Matrix
coordinates = [xx(:) yy(:)] ;
NodeNo = 1:nnode ;
nodes = zeros(nel,nnel) ;
% If elements along the X-axes and Y-axes are equal
if npx==npy
    NodeNo = reshape(NodeNo,npx,npy);
    nodes(:,1) = reshape(NodeNo(1:npx-1,1:npy-1),nel,1);
    nodes(:,2) = reshape(NodeNo(2:npx,1:npy-1),nel,1);
    nodes(:,3) = reshape(NodeNo(2:npx,2:npy),nel,1);
    nodes(:,4) = reshape(NodeNo(1:npx-1,2:npy),nel,1);
end
%
% Plotting the Finite Element Mesh
% Initialization of the required matrices
X = zeros(nnel,nel) ;
Y = zeros(nnel,nel) ;
% Extract X,Y coordinates for the (iel)-th element
  for iel = 1:nel
      X(:,iel) = coordinates(nodes(iel,:),1) ;
      Y(:,iel) = coordinates(nodes(iel,:),2) ;
  end 
% Figure
fh = figure ;
set(fh,'name','Preprocessing for FEA','numbertitle','off','color','w') ;
patch(X,Y,'w')
title('Finite Element Mesh of Plate') ;
axis([0. L*1.01 0. B*1.01])
axis off ;
if L==B
    axis equal ;
end

[Kevin Chng]

We take a look at this line first

X(:,iel) = coordinates(nodes(iel,:),1) ;

put display(iel) infront of this line

display(iel)  
X(:,iel) = coordinates(nodes(iel,:),1) ;

iel is indeces, it must be real positive integers or logical. Therefore, 0, negative value, floating value are not allowed.

[madhan ravi]

    X(iel,:) = coordinates(nodes(iel,:),1) ;

X(:,iel) -> this is wrong

    coordinates(nodes(iel,:),1) %error is because of this

[zainab malik]

If i am considering 8 nodes, do i have to define other 4 nodes location or its just fine?;

if true
  % code
if npx==npy
  NodeNo = reshape(NodeNo,npx,npy);
  nodes(:,1) = reshape(NodeNo(1:npx-1,1:npy-1),nel,1);
  nodes(:,2) = reshape(NodeNo(2:npx,1:npy-1),nel,1);
  nodes(:,3) = reshape(NodeNo(2:npx,2:npy),nel,1);
  nodes(:,4) = reshape(NodeNo(1:npx-1,2:npy),nel,1);

[zainab malik]

If for 8 nodes I add four more nodes like:

if true
  % code
  nodes(:,1) = reshape(NodeNo(1:npx-1,1:npy-1),nel,1);
  nodes(:,2) = reshape(NodeNo(2:npx,1:npy-1),nel,1);
  nodes(:,3) = reshape(NodeNo(2:npx,2:npy),nel,1);
  nodes(:,4) = reshape(NodeNo(1:npx-1,2:npy),nel,1);
  nodes(:,5) = reshape(NodeNo(1:npx-1,1:npy-1),nel,1);
  nodes(:,6) = reshape(NodeNo(2:npx,1:npy-1),nel,1);
  nodes(:,7) = reshape(NodeNo(2:npx,2:npy),nel,1);
  nodes(:,8) = reshape(NodeNo(1:npx-1,2:npy),nel,1);

I dont get any error but can someone explain that is that ok what i define ?

[Kevin Chng]

I think your error is from here

nodes(iel,:)

first you assign zero to nodes with 400 x 8 dimension

nodes = zeros(nel,nnel) ;

later in your reshape you assign dimension 21*21 to NodeNo

NodeNo = reshape(NodeNo,npx,npy);

Then reshape nodes follow below

nodes(:,1) = reshape(NodeNo(1:npx-1,1:npy-1),nel,1);

that's mean now nodes(:,1) has dimesion 441 * 1 then you do similar thing to nodes(:,2), nodes(:,3), nodes(:,4).

Now, Try to think, what is the dimension of nodes(:,5)? originally, you assign zero to nodes(:,5) from 1 to 400, then with new expansion of your nodes, 401 to 441 will be NaN.

At the end

X(:,iel) = coordinates(NaN,1) ;

So how to solve it ? I guess simply to change this line to 21*21 dimension

nodes = zeros(npx,npy) ; % your npx is 21 dimension, npy is also 21 dimension

[zainab malik]

Thank you KevinChng Sir!! Could you please help me also in this that when I try to display node and element number by adding the below lines at the end of node.

if true
  % code
% To display Node Numbers % Element Numbers
pos = [70 20 60 20] ;
ShowNodes = uicontrol('style','toggle','string','nodes','value',0,....
  'position',[pos(1) pos(2) pos(3) pos(4)],'background','white','callback',...
  @(varargin) SHOWN(ShowNodes,ShowElements,coordinates,X,Y,nnode,nel,nodes));
pos = get(ShowNodes,'position') ;
pos = [2*pos(1) pos(2) pos(3) pos(4)] ;
ShowElements = uicontrol('style','toggle','string','Elements','value',0,.... 
  'position',[pos(1) pos(2) pos(3) pos(4)],'background','white','callback',....
  @(varargin) SHOWELEMENTS(ShowElements,ShowNodes,coordinates,X,Y,nel,nodes,nnode));

I get

Error : Undefined function or variable 'SHOWNODES'. Error while evaluating UIControl Callback

How I resolve this?

[Kevin Chng]

Hi,

at my first glance, your error is

'callback',...
  @(varargin) SHOWN(ShowNodes,ShowElements,coordinates,X,Y,nnode,nel,nodes)

I'm not really remember how to write the syntax to pass argument for callback. Usually, i will use handles and pass the handles to the callback function. More information, you can refer to link below:

https://www.mathworks.com/help/matlab/creating_guis/share-data-among-callbacks.html#bt9p4s2

However,

1st) ShowElemet has yet declared, you can't put him into the argument pass to your callback function

2nd) Put the object name into his own callback function, i guess it is not a proper way to do. Refer to code below on how to get your uicontrol object information.

slider = uicontrol('Parent', hfig,'Style','slider',...
         'Units','normalized',...
         'Position',[0.3 0.5 0.4 0.1],...
         'Tag','slider1',...
         'Callback',@slider_callback);

function slider_callback(hObject,eventdata)
  data = guidata(hObject);
  data.val = hObject.Value;
  data.diffMax = hObject.Max - data.val;
  % For R2014a and earlier:
  % data.val = get(hObject,'Value');
  % maxval = get(hObject,'Max');
  % data.diffMax = maxval - data.val;

  guidata(hObject,data);
end

Refer to code above, in your callback function, you simply use guidata(hObject) to get the information of your slider.

Answer 1

[Kevin Chng]

I think your error is from here

nodes(iel,:)

first you assign zero to nodes with 400 x 8 dimension

nodes = zeros(nel,nnel) ;

later in your reshape you assign dimension 21*21 to NodeNo

NodeNo = reshape(NodeNo,npx,npy);

Then reshape nodes follow below

nodes(:,1) = reshape(NodeNo(1:npx-1,1:npy-1),nel,1);

that's mean now nodes(:,1) has dimesion 441 * 1 then you do similar thing to nodes(:,2), nodes(:,3), nodes(:,4).

Now, Try to think, what is the dimension of nodes(:,5)? originally, you assign zero to nodes(:,5) from 1 to 400, then with new expansion of your nodes, 401 to 441 will be NaN.

At the end

X(:,iel) = coordinates(NaN,1) ;

So how to solve it ? I guess simply to change this line to 21*21 dimension

nodes = zeros(npx,npy) ;

% your npx is 21 dimension, npy is also 21 dimension

Answer 2

[Image Analyst]

I think it's pretty well explained by the FAQ: https://matlab.wikia.com/wiki/FAQ#How_do_I_fix_the_error_.22Subscript_indices_must_either_be_real_positive_integers_or_logicals..22.3F