I am very new to MATLAB but I have to deliver an assignment. How do I solve matrix dimension issue in line 10 and 11.

Question

Frederick Kwame 2024-6-11

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https://ww2.mathworks.cn/matlabcentral/answers/2127696-i-am-very-new-to-matlab-but-i-have-to-deliver-an-assignment-how-do-i-solve-matrix-dimension-issue-i

评论： Frederick Kwame 2024-6-12

采纳的回答： Walter Roberson

Given the following matrix dimensions

L=39360*39360

y=39360*1

q=1*39360

E= 2.8709

X=39360*39360

T=39360*39360

code

1. dq=L*y;

2. dtr=dq.*q'/E;

3. ql = q * L;

4. ldf = L * y;

5. dt = zeros(39360, 39360);

6. dtr = zeros(39360, 39360);

7. for a = 1:39360

8. for b = 1:39360

9. if X(b, :) ~= 0

10. dt(a,b) = ql(:,a)*ldf(b,:) /X(b,:);

11. dtr(a,b) = (ql(:,a)*ldf(b,:)* T))/(X(b,:)*E);

else

dt(a, b) = 0;

dtr(a, b) = 0;

end

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Walter Roberson 2024-6-11

在 MATLAB Online 中打开

N = 39360;
L = rand(N, N);
y = rand(N, 1);
q = rand(1, N);
E = 2.8709;
X = rand(N, N);
T = rand(N, N);
dq=L*y;
dtr=dq.*q'/E;
ql = q * L;
ldf = L * y;
dt = zeros(39360, 39360);
dtr = zeros(39360, 39360);
for a = 1:39360
    for b = 1:39360
        if X(b, :) ~= 0
           dt(a,b) = ql(:,a)*ldf(b,:) /X(b,:); 
           dtr(a,b) = (ql(:,a)*ldf(b,:)* T))/(X(b,:)*E);

1 0 1 2 1 2 1 0? 0 1 0 ?

 
        else
            dt(a, b) = 0;
            dtr(a, b) = 0;
        end
    end
end

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Answer 1

Walter Roberson 2024-6-11

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移动：Walter Roberson 2024-6-11

在 MATLAB Online 中打开

Your ldf is 39360 x 1. Your ql is 1 x 3936. Select rows and columns out of those and you get 1 x 1 and 1 x 1. Use * to multiply two 1 x 1 and you get 1 x 1. You cannot / between 1 x 1 and a 1 x something (not unless the "something" is 1)

%N = 39360;      %too large for actual test
N = 3936;
L = rand(N, N);
y = rand(N, 1);
q = rand(1, N);
E = 2.8709;
X = rand(N, N);
T = rand(N, N);
dq=L*y;
dtr=dq.*q'/E;
ql = q * L;
ldf = L * y;
whos ql ldf
  Name         Size              Bytes  Class     Attributes

  ldf       3936x1               31488  double              
  ql           1x3936            31488  double              
dt = zeros(N, N);
dtr = zeros(N, N);
for a = 1:N
    for b = 1:N
        if X(b, :) ~= 0
           temp1 = ql(:,a);
           temp2 = ldf(b,:);
           temp3 = temp1 * temp2;
           temp4 = X(b,:);
           whos temp1 temp2 temp3 temp4
           dt(a,b) = temp3 / temp4;
           temp4 = (ql(:,a)*ldf(b,:)* T);
           temp5 = (X(b,:)*E);
           whos temp4 temp5
           dtr(a,b) = (ql(:,a)*ldf(b,:)* T)/(X(b,:)*E);
        else
            dt(a, b) = 0;
            dtr(a, b) = 0;
        end
    end
end           
  Name       Size              Bytes  Class     Attributes

  temp1      1x1                   8  double              
  temp2      1x1                   8  double              
  temp3      1x1                   8  double              
  temp4      1x3936            31488  double              
Error using /
Matrix dimensions must agree.