issue creating loop with matrix multiplication

Hi. I'm quite new to Matlab, and have a project, and am stuck on trying to run a loop. I'm trying to solve for the lat/lon/height of a sonar system. I've been given the GPS Lat/Lon and pitch, roll, yaw and heave from the sensor, as well as their relative offsets. I've started with this, and can get it run successfully once , but can't get it to loop for all the records in my file (~500). thanks in advance.

for i = 1:length (roll)
     matRotZ = [cos(heading(i)) -sin(heading(i)) 0; sin(heading(i)) cosd(heading(i)) 0; 0 0 1];
     matRotY = [cos(pitch(i)) 0 sin(pitch(i)); 0 1 0; -sin(pitch(i)) 0 cosd(pitch(i))];
     matRotX = [1 0 0; 0 cos(roll(i)) -sin(roll(i)); 0 sin(roll(i)) cosd(roll(i))];

% Tait-bryan matrix multiplication.  
     RotAll = matRotZ * matRotY * matRotX;

       PosRotated =  RotAll * [X; Y; Z];
  % [X; Y ; Z] is the offset of the instrument from Reference Point.

end

Answer 1

[Matt Fig]

What are you trying to save out of the loop? If you want to save the RotAll for each element of heading, pitch and roll, do:

RotAll{i} = matRotZ * matRotY * matRotX;

Of course you will then have to change the next line to:

PosRotated =  RotAll{i} * [X; Y; Z];

[Matt Fig]

Dana commented:

"Hi, I'd like RotAll, for each, but am ultimately interested in PosRotated... So, based on your input, I could do this?

RotAll(i) = matRotZ * matRotY * matRotX; 
PosRotated(i) = RotAll * [X; Y; Z];

I shall give it a try, thank you. Dana"

[Matt Fig]

No!

Look at the difference:

RotAll(i)  % Your code
RotAll{i}  % My code  {}, not ()

The way I wrote it, your RotAll will be a cell array, which is how you store many different elements of different sizes. Look at this example:

C{1} = magic(2);
C{2} = [1 2 3];
C{3} = 4;
% Now examine the contents with:
C{1}

If you want to save PosRotated for each iteration also, you will have to make that a cell too.

[Matt Fig]

Dana comments (again as an Answer!):

"ok, I see, thanks. however, I'm getting an error when I use:

RotAll{i} = matRotZ * matRotY * matRotX;

I get the following Error:

Cell contents assignment to a non-cell array object. Error in EM_Matrix_New (line 21) RotAll{i} = matRotZ * matRotY * matRotX;"

[Matt Fig]

If you are getting that error than either you forgot to clear a RotAll from the workspace because you are running a script or there is more to your code than you showed because I get no such error just using your code snippet.