??? Index exceeds matrix dimensions.

31 Jul 2012
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I keep getting this error every time I run this code. Can you tell me where I am wrong? I have run through the debugger and can't seem to figure out where I went wrong.
K = zeros(3*NN,3*NN);
M = zeros(3*NN,3*NN);
for n = 1:NE
i = Dir(n,2);
j = Dir(n,3);
K(3*i-2:3*i,3*i-2:3*i)= K11(:,:,n) + K(3*i-2:3*i,3*i-2:3*i);
K(3*i-2:3*i,3*j-2:3*j)= K12(:,:,n);
K(3*j-2:3*j,3*i-2:3*i)= K21(:,:,n);
K(3*j-2:3*j,3*j-2:3*j)= K22(:,:,n) + K(3*j-2:3*j,3*j-2:3*j);
M(3*i-2:3*i,3*i-2:3*i)= M11(:,:,n) + M(3*i-2:3*i,3*i-2:3*i);
M(3*i-2:3*i,3*j-2:3*j)= M12(:,:,n);
M(3*j-2:3*j,3*i-2:3*i)= M21(:,:,n);
M(3*j-2:3*j,3*j-2:3*j)= M22(:,:,n) + M(3*j-2:3*j,3*j-2:3*j);
end

3 Comments
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Azzi Abdelmalek
Azzi Abdelmalek on 31 Jul 2012
Edited: Azzi Abdelmalek on 31 Jul 2012
what are NN NE Dir,..?
Walter Roberson
Walter Roberson on 31 Jul 2012
Azzi is right: the information you have given us does not allow us to determine whether 3*i-2 to 3*i and 3*j-2 to 3*j are within the size of K and M; we also cannot tell that the third dimension of K* and M* are at least as big as NE.
Jonathan
Jonathan on 31 Jul 2012
Thank you for your suggestions. I am a nubie at Matlab and I'm trying to learn it as fast as I can. In response to your questions, NN and NE are the number of nodes and number of elements respectively.
I will try to post most of the code for you to see what I'm talking about.
NN = xlsread('test','Input','B2');
coord = xlsread('test','Input','A4:C8');
for j = 1:NN
i = coord(j,1);
x(i) = coord(j,2);
y(i) = coord(j,3);
% plot(x,y)
% hold on
end
NE = xlsread('test','Input','F2');
Pro = xlsread('test','Input','E4:K7');
for j = 1:NE
i = Pro(j,1);
I(i) = Pro(j,4);
A(i) = Pro(j,5);
E(i) = Pro(j,6);
m_bar(i) = Pro(j,7);
Dir(i,1) = i;
Dir(i,2) = Pro(j,2);
Dir(i,3) = Pro(j,3);
end
NC = xlsread('test','Input','N2');
cons = xlsread('test','Input','M4:O6');
for i = 1:NE
L(i) = sqrt((x(Dir(i,3))-(x(Dir(i,2))))^2 + (y(Dir(i,3))-(y(Dir(i,2))))^2);
Cos(i) = ((x(Dir(i,3))-(x(Dir(i,2)))))/L(i);
Sin(i) = ((y(Dir(i,3))-(y(Dir(i,2)))))/L(i);
end
mass_kind = 0;
for i = 1:NE
S(i) = (E(i)*A(i))/L(i)^3;
k11(:,:,i) = S(i)*[A(i)*L(i)^2/I(i) 0 0;0 12 6*L(i);0 6*L(i) 4*L(i)^2];
k12(:,:,i) = S(i)*[-A(i)*L(i)^2/I(i) 0 0;0 -12 6*L(i);0 -6*L(i) 2*L(i)^2];
k21(:,:,i) = S(i)*[-A(i)*L(i)^2/I(i) 0 0;0 -12 -6*L(i);0 6*L(i) 2*L(i)^2];
k22(:,:,i) = S(i)*[A(i)*L(i)^2/I(i) 0 0;0 12 -6*L(i);0 -6*L(i) 4*L(i)^2];
if mass_kind == 0
Q(i) = m_bar(i)*L(i)/420;
m11(:,:,i) = Q(i)*[140 0 0;0 156 22*L(i);0 22*L(i) 4*L(i)^2];
m12(:,:,i) = Q(i)*[70 0 0;0 54 -13*L(i);0 13*L(i) -3*L(i)^2];
m21(:,:,i) = Q(i)*[70 0 0;0 54 13*L(i);0 -13*L(i) -3*L(i)^2];
m22(:,:,i) = Q(i)*[140 0 0;0 156 -22*L(i);0 -22*L(i) 4*L(i)^2];
else
Q(i) = m_bar(i)*L(i)/2;
m11(:,:,i) = Q(i)*eye(3,3); m11(3,3,i) = 0;
m12(:,:,i) = Q(i)*eye(3,3);
m21(:,:,i) = Q(i)*eye(3,3);
m22(:,:,i) = Q(i)*eye(3,3); m22(3,3,i) = 0;
end
end
for n = 1:NE
T(:,:,n) = [Cos(n) Sin(n) 0;-Sin(n) Cos(n) 0;0 0 1];
for i = 1:3
for j = 1:3
Tt(i,j,n) = T(j,i,n);
end
end
end
for i = 1:NE
K11 = Tt(:,:,i)*k11(:,:,i)*T(:,:,i);
K12 = Tt(:,:,i)*k12(:,:,i)*T(:,:,i);
K21 = Tt(:,:,i)*k21(:,:,i)*T(:,:,i);
K22 = Tt(:,:,i)*k22(:,:,i)*T(:,:,i);
M11 = Tt(:,:,i)*m11(:,:,i)*T(:,:,i);
M12 = Tt(:,:,i)*m12(:,:,i)*T(:,:,i);
M21 = Tt(:,:,i)*m21(:,:,i)*T(:,:,i);
M22 = Tt(:,:,i)*m22(:,:,i)*T(:,:,i);
end
K = zeros(3*NN,3*NN);
M = zeros(3*NN,3*NN);
for n = 1:NE
i = Dir(n,2);
j = Dir(n,3);
K(3*i-2:3*i,3*i-2:3*i)= K11(:,:,n) + K(3*i-2:3*i,3*i-2:3*i);
K(3*i-2:3*i,3*j-2:3*j)= K12(:,:,n);
K(3*j-2:3*j,3*i-2:3*i)= K21(:,:,n);
K(3*j-2:3*j,3*j-2:3*j)= K22(:,:,n) + K(3*j-2:3*j,3*j-2:3*j);
M(3*i-2:3*i,3*i-2:3*i)= M11(:,:,n) + M(3*i-2:3*i,3*i-2:3*i);
M(3*i-2:3*i,3*j-2:3*j)= M12(:,:,n);
M(3*j-2:3*j,3*i-2:3*i)= M21(:,:,n);
M(3*j-2:3*j,3*j-2:3*j)= M22(:,:,n) + M(3*j-2:3*j,3*j-2:3*j);
end

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 Accepted Answer

Jan
Jan on 31 Jul 2012
Edited: Jan on 31 Jul 2012

1 vote

Use the debugger again:
dbstop if error
Then start the code. Matlab stops when the error occurs and you can evaluate the parts of the currently processed line in the command window, e.g.:
K11(:, :, n)
K(3*i-2:3*i, 3*i-2:3*i)
Then you will find out, which of the statements cause the error. Btw. the responsible line is shown in the error message also, and therefore it is a good idea to post the complete error messages, if you want help in the forum.
Another hint: If you use temporary variables for the index expressions, the code will look cleaner:
a = 3*i-2;
b = 3*i;
c = 3*j-2;
d = 3*j;
Beside the reduction of runtime, the improved readability will allow for an easier debugging.

3 Comments
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Jonathan
Jonathan on 31 Jul 2012
Thank you for your suggestions. I will try to clean up the code so its easier to read.
Jonathan
Jonathan on 31 Jul 2012
Here is the cleaned up version of code.
dbstop if error
%input data
NN = xlsread('test','Input','B2'); %Input Number of Nodes
coord = xlsread('test','Input','A4:C8'); %Coordinates
for j = 1:NN
i = coord(j,1);
x(i) = coord(j,2);
y(i) = coord(j,3);
% plot(x,y) %Plots OK
% hold on
end
NE = xlsread('test','Input','F2'); %Number of Elements
Pro = xlsread('test','Input','E4:K7'); %Properties of Elements
for j = 1:NE
i = Pro(j,1);
I(i) = Pro(j,4);
A(i) = Pro(j,5);
E(i) = Pro(j,6);
m_bar(i) = Pro(j,7);
Dir(i,1) = i;
Dir(i,2) = Pro(j,2);
Dir(i,3) = Pro(j,3);
end
NC = xlsread('test','Input','N2'); %Number of Constraints
cons = xlsread('test','Input','M4:O6'); %Constraints
%Length of Elements
for i = 1:NE
L(i) = sqrt((x(Dir(i,3))-(x(Dir(i,2))))^2 + (y(Dir(i,3))-(y(Dir(i,2))))^2);
Cos(i) = ((x(Dir(i,3))-(x(Dir(i,2)))))/L(i);
Sin(i) = ((y(Dir(i,3))-(y(Dir(i,2)))))/L(i);
end
%Insert here for nodal loads
mass_kind = 0;
%Element Stiffness/Mass Matrics
for i = 1:NE
S(i) = (E(i)*A(i))/L(i)^3;
k11(:,:,i) = S(i)*[A(i)*L(i)^2/I(i) 0 0;0 12 6*L(i);0 6*L(i) 4*L(i)^2];
k12(:,:,i) = S(i)*[-A(i)*L(i)^2/I(i) 0 0;0 -12 6*L(i);0 -6*L(i) 2*L(i)^2];
k21(:,:,i) = S(i)*[-A(i)*L(i)^2/I(i) 0 0;0 -12 -6*L(i);0 6*L(i) 2*L(i)^2];
k22(:,:,i) = S(i)*[A(i)*L(i)^2/I(i) 0 0;0 12 -6*L(i);0 -6*L(i) 4*L(i)^2];
if mass_kind == 0
Q(i) = m_bar(i)*L(i)/420;
m11(:,:,i) = Q(i)*[140 0 0;0 156 22*L(i);0 22*L(i) 4*L(i)^2];
m12(:,:,i) = Q(i)*[70 0 0;0 54 -13*L(i);0 13*L(i) -3*L(i)^2];
m21(:,:,i) = Q(i)*[70 0 0;0 54 13*L(i);0 -13*L(i) -3*L(i)^2];
m22(:,:,i) = Q(i)*[140 0 0;0 156 -22*L(i);0 -22*L(i) 4*L(i)^2];
else
Q(i) = m_bar(i)*L(i)/2;
m11(:,:,i) = Q(i)*eye(3,3); m11(3,3,i) = 0;
m12(:,:,i) = Q(i)*eye(3,3);
m21(:,:,i) = Q(i)*eye(3,3);
m22(:,:,i) = Q(i)*eye(3,3); m22(3,3,i) = 0;
end
end
%Transformation Matrices
for n = 1:NE
T(:,:,n) = [Cos(n) Sin(n) 0;-Sin(n) Cos(n) 0;0 0 1];
for i = 1:3
for j = 1:3
Tt(i,j,n) = T(j,i,n);
end
end
end
%Transformation from Local to Global Coordinates
for i = 1:NE
K11 = Tt(:,:,i)*k11(:,:,i)*T(:,:,i);
K12 = Tt(:,:,i)*k12(:,:,i)*T(:,:,i);
K21 = Tt(:,:,i)*k21(:,:,i)*T(:,:,i);
K22 = Tt(:,:,i)*k22(:,:,i)*T(:,:,i);
M11 = Tt(:,:,i)*m11(:,:,i)*T(:,:,i);
M12 = Tt(:,:,i)*m12(:,:,i)*T(:,:,i);
M21 = Tt(:,:,i)*m21(:,:,i)*T(:,:,i);
M22 = Tt(:,:,i)*m22(:,:,i)*T(:,:,i);
end
%Global/Mass Matrices
K = zeros(3*NN,3*NN);
M = zeros(3*NN,3*NN);
for n = 1:NE
i = Dir(n,2);
j = Dir(n,3);
a = 3*i-2;
b = 3*i;
c = 3*j-2;
d = 3*j;
K(a:b,a:b)= K11(:,:,n) + K(a:b,a:b);
K(a:b,c:d)= K12(:,:,n);
K(c:d,a:b)= K21(:,:,n);
K(c:d,c:d)= K22(:,:,n) + K(c:d,c:d);
M(a:b,a:b)= M11(:,:,n) + M(a:b,a:b);
M(a:b,c:d)= M12(:,:,n);
M(c:d,a:b)= M21(:,:,n);
M(c:d,c:d)= M22(:,:,n) + M(c:d,c:d);
end
Jonathan
Jonathan on 31 Jul 2012
The error message as shown in the command window. I appreciate your help with this program.
??? Index exceeds matrix dimensions.
Error in ==> main3 at 100
K(a:b,a:b)= K11(:,:,n) + K(a:b,a:b);

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Jonathan
Jonathan
on 31 Jul 2012

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