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Matrix Dimensions must agree

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Kane Patrick Bobier
Kane Patrick Bobier on 19 Oct 2020
Hi everyone, I am having trouble getting my code to run. (Specifically line 71, inside the for loop GK). I don't get it because I use a similar code in line 51-58:
clc;
clear;
close all;
prompt = 'Specifiy Node Value';
N = input(prompt)
A1 = 0.05;
K1 = 125;
L1 = 0.6;
Q1 = 0;
A2 = 0.08;
K2 = 80;
L2 = 0.7;
Q2 = 100;
A3 = 0.7;
K3 = 100;
L3 = 0.2;
Q3 = 0;
A4 = 0.01;
K4 = 150;
L4 = 0.5;
Q4 = 200;
NS = N/4
NS = round(NS)
NES = NS-2
K1 = ((A1*K1)/L1)*[1,-1;-1,1];
K2 = ((A2*K2)/L2)*[1,-1;-1,1];
K3 = ((A3*K3)/L3)*[1,-1;-1,1];
K4 = ((A4*K4)/L4)*[1,-1;-1,1];
GK1 = zeros(NES+1,NES+1);
GK2 = zeros(NES+1,NES+1);
GK3 = zeros(NES+1,NES+1);
GK4 = zeros(NES+1,NES+1);
GK5 = zeros(N,N);
for k = 1:NES,
GK1(k:k+1,k:k+1) = (GK1(k:k+1,k:k+1)+K1);
GK2(k:k+1,k:k+1) = (GK2(k:k+1,k:k+1)+K2);
GK3(k:k+1,k:k+1) = (GK3(k:k+1,k:k+1)+K3);
GK4(k:k+1,k:k+1) = (GK4(k:k+1,k:k+1)+K4);
end
GK1
GK2
GK3
GK4
ProtoGK = {GK1,GK2,GK3,GK4};
Nu = numel(ProtoGK);
Nu
GK = zeros(1+Nu,1+Nu);
for k = 1:Nu,
GK(k:k+1,k:k+1) = (GK(k:k+1,k:k+1) + ProtoGK{k});
end
GK
  2 Comments
KSSV
KSSV on 19 Oct 2020
You need to rethink on your code.....it completely looks meaning less...
Kane Patrick Bobier
Kane Patrick Bobier on 19 Oct 2020
This code is for a stiffness matrix of a rod with four elements. I just need help putting together the final global stiffness matrix.

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Answers (1)

Asad (Mehrzad) Khoddam
Asad (Mehrzad) Khoddam on 19 Oct 2020
change the varibales to vector form:
A=[0.05, 0.08, 0.7, 0.01];
E=[125, 80, 100, 150];
L=[0.6, 0.7, 0.2, 0.5];
ndof=length(A)+1;
KG = zeros(ndof, ndof);
for i = length(A)
k=A(i)*E(i)/L(i) * [1, -1; -1, 1]
dof = [i, i+1];
KG(dof, dof) = KG(dof, dof) + k;
end
  2 Comments
Kane Patrick Bobier
Kane Patrick Bobier on 19 Oct 2020
Where should I place this? Thank you for the reply!
Asad (Mehrzad) Khoddam
Asad (Mehrzad) Khoddam on 19 Oct 2020
Replace your code with the new one, I modified some parts,
A=[0.05, 0.08, 0.7, 0.01];
E=[125, 80, 100, 150];
L=[0.6, 0.7, 0.2, 0.5];
Q=[0, 100, 0, 200];
ndof=length(A)+1;
KG = zeros(ndof, ndof);
for i = 1:length(A)
k=A(i)*E(i)/L(i) * [1, -1; -1, 1];
dof = [i, i+1];
KG(dof, dof) = KG(dof, dof) + k;
end
KG

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