Transformation matrix 3d beam: I have to do a function for a 3D beam structure 90 degrees rotation of the global to local axes. (the two beams are perpendicular to each other). This function appears to be correct but appears error in driver file.

function T = transformation2(x1,y1,z1,x2,y2,z2,omega)

     L=sqrt((x2-x1)^2+(y2-y1)^2+(z2-z1)^2);    % element length
      Cx = (x2-x1)/L;     %%%direction cosine 
      Cy = (y2-y1)/L;     %%%direction cosine 
      Cz = (z2-z1)/L;     %%%direction cosine 
      co = cos(omega);
      so = sin(omega);

    Cxz = sqrt(Cx^2 + Cz^2);
          T1 = [  Cx                        Cy                Cz
               -(Cx*Cy*co+Cz*so)/Cxz     Cxz*co   -(Cy*Cz*co+Cx*so)/Cxz
                (Cx*Cy*so-Cz*co)/Cxz    -Cxz*so    (Cy*Cz*so+Cx*co)/Cxz];

            T=[ T1 0 0 0;...
                0 T1 0 0;...
                0 0 T1 0;...
                0 0 0 T1];

end

[Walter Roberson]

And what error is it that appears in the driver file?

[Sean de Wolski]

omega is in radians, right?

[Michael]

omega is the dihedral angle and is in radians yes....the error is :Error in ==> transformation2 at 17

L=sqrt((x2-x1)^2+(y2-y1)^2+(z2-z1)^2); % element length

Answer 1

[Walter Roberson]

You are going to get horzcat or vertcat dimension mismatches. Your T1 is 3 x 3, but you use it as if it were a 1 x 1 when you construct T.

You should possibly be using blkdiag() to construct the T array:

T = blkdiag(T1,T1,T1,T1);

[Michael]

T should be a 12x12 matrix..so 0 is a null matrix..i forgot to mention it.Thank you

[Walter Roberson]

You still have not said what the error message is, just where it is.

If your x1, x2, etc., are vectors, then you would need to use .^2 rather than ^2 . In turn, that would make L a vector, and then in the C[xyz] lines following you would probably want to use ./ instead of / and likewise when constructing T1 .

Your saying that T will come out 12 by 12 implies that you are expecting the C[xyz] variables to come out as 4 x 4 arrays.

[Michael]

T1 = matrix 3x3 and T = matrix 12x12 cause T has diagonal matrices T1 like what you set before T = blkdiag(T1,T1,T1,T1);

When I run driver file appears error on line 115 which is the function and when I run just the function to check it, appears on Element Length (L) ,the second line.

Thank you man for the help!

[Sean de Wolski]

What is the error message?

[Walter Roberson]

I agree, we need the error message text, not just to know which line it is on.

[Michael]

??? Input argument "x2" is undefined.

Error in ==> transformation2 at 4

L=sqrt((x2-x1).^2+(y2-y1).^2+(z2-z1).^2); % element length

sorry man :)

[Michael]

we've tried to solve it with this way also:

function T=Transformation2(x1,y1,z1,x2,y2,z2,omega)

omega= omega*pi/180; % convert omega to radians

length=sqrt((x2-x1)^2+(y2-y1)^2+(z2-z1)^2);

lx=(x2-x1)/length;

mx=(y2-y1)/length;

nx=(z2-z1)/length;

ax=acos(lx);

bx=acos(mx);

dx=acos(nx);

ux=x2-x1;

uz=z2-z1;

if ux==0 %check in case denominator is zero

ro = pi/2; %degrees

else

ro=-atan(uz/ux);

end

xi=(0.5*pi-bx);

g1= [ 1 0 0 ;...

0 cos(omega) sin(omega);...

0 -sin(omega) cos(omega)];...

g2= [cos(xi) sin(xi) 0;...

-sin(xi) cos(xi) 0;...

0 0 1];...

g3= [cos(ro) 0 -sin(ro);...

0 1 0;...

sin(ro) 0 cos(ro)];...

gamma=g1*g2*g3;

ga=[gamma gamma gamma;...

gamma gamma gamma];...

zero=[0 0 0; ...

0 0 0];...

T= [ga zero zero zero;...

zero ga zero zero;...

zero zero ga zero;...

zero zero zero ga];...

end

[Sean de Wolski]

how are you calling it? Are you passing in four input arguments?

[Michael]

sorry I didn't understand what you mean by passing in four input arguments..

[Walter Roberson]

Your error would be consistent with you having started the program by pressing F5 or using the menu "run" command, or typing Transformation2 in to the command line and then pressing return.

What you need to do, is on the command line type

Transformation2(1,2,3,4,5,6,7)

except that you need to replace the 1 with the value you want for x1, replace the 2 with the value you want for y1, the 3 with the value for z1, the 4 with the value for x2, and so on.

Transformation2(rand(3,15), ... )

or whatever is appropriate for you situation.

[Sean de Wolski]

What line of code do you use to call |Transformation2|?

I would guess it's not

T = Transformation2(10,10,10,20,20,20,pi/2) %or similar

i.e. 7 inputs - what is required. The reason I asked if you were passing at least four is because the error message says 'x2' is not defined and x2 is the fourth input argument. y1,z1 might also be undefined though. This would also mean you don't have the 'omega = omega*pi/180' line since that would mean you _are_ passing in seven arguments. Please edit your original question to reflect what you currently have, how you're calling the function, and the full text of the error message.