Error using * Matrix dimensions must agree. please help.

 N_BF=10;
 N_s=700;
  A1=zeros(N_BF,N_BF);
  Wu=zeros(N_BF,N_BF);
  Ww=zeros(N_BF,N_BF);
  b1=zeros(N_BF,1);

 % compute interval
 t2=cputime;
 for i=1:N_s
 x1=-1300+rand; x2=0+rand; x3=0+rand;
 f=[x2/x3; -x1*x2/x3; x1];
 BF=[ x1^2;  x1*x2;  x1*x3;  x2^2  ;x2*x3 ; x3^2 ;
      x1/x3;  x1*x2/x3 ; x2^2/x3 ; x2^4/x3^2];
 DBF= [ 2*x1    0         0
        x2      x1        0
        x3      0         x1
        0       2*x2      0
        0       x3        x2 
        0       0         2*x3
        1/x3    0         -x1/x3^2
        x2/x2   x1/x3     -x1*x2/x3^2
        0       2*x2/x3   -x2^2/x3^2
        0       4*x2^3    -2*x2^4/x3^3];

    Aa=[x1;x2;x3]'*[x1;x2;x3];
    A1=A1+BF*f'*DBF';
    b1=b1+BF*Aa;

    g1=[0;1;0]';
    g2=[0;-1;0]';

    for j= 1:N_BF

       Wu(:,:,j)=Wu(:,:,j)+BF*DBF(j,:)*g2*g2'*DBF';
       Ww(:,:,j)=Ww(:,:,j)+BF*DBF(j,:)*g1*g1'*DBF';
    end

 end
getting the error at Wu(:,:,j)=Wu(:,:,j)+BF*DBF(j,:)*g2*g2'*DBF';

Answer 1

[Abhiram Bhanuprakash]

Hi JJ Kena,

I think the error is because one row of DBF is 1X3, and g2 is also 1X3. So, when it tries to multiply both of them, you get the dimension mismatch error.

Paranthesizing the g2*g2' term would resolve the issue.

Thus, change the two lines of code to:

Wu(:,:,j)=Wu(:,:,j)+BF*DBF(j,:)*(g2*g2')*DBF';
Ww(:,:,j)=Ww(:,:,j)+BF*DBF(j,:)*(g1*g1')*DBF';

and you would be able to run it.

Also, if you observe, MATLAB shows an orange symbol in the Editor window for the two lines, and if you hover over it, you can see a message which says 'Paranthesize the multiplication to ensure the result is Hermitian'.

Hope this resolves your issue. MATLAB rocks!

Cheers!

[jj kena]

Abhiram Bhanuprakash, thanks alot, did that n saw another problem too, its at

Wu=zeros(N_BF,N_BF); Ww=zeros(N_BF,N_BF); these two shlould be, Wu=zeros(N_BF,N_BF,N_BF); Ww=zeros(N_BF,N_BF,N_BF);

Answer 2

[yonatan gerufi]

well, your line:

Wu(:,:,j)=Wu(:,:,j)+BF*DBF(j,:)*g2*g2'*DBF';

is totally messed up with dimension.

think what dimentions each parameter should be, and see the difference with debug mode.

saying all that, pay attention that if you want element-by-element multiplication you should use "."

e.g. A.*B

good luck.

Answer 3

[jj kena]

yonatan gerufi ,from BF*DBF(j,:)*g2*g2'*DBF', BF is 10x1, BDF(j,:) is 1x3, g2 is 3x1, g2' is 1x3, and DBF' is 3x10, if i think you can multiply those matrices without a problem to give u a 10x10 matrice.