multiplication of matrix with long data

Hi,

I have a long data (200K+ samples) from which a location vector L (3x1) and a matrix T (euler matrix 3x3) is generated and multiplied l = TL.

On the results of l (3x1) there are operations of sin and atan (to get the required results).

So far, I'm doing a for loop, which is not a Matlab way.

I'd like to speedup the performance of the code.

How can I do it?

[Walter Roberson]

What are you looping? The only part that you describe that involves the large data is the creation of L and T, and you do not describe the math involved in that.

Are you looping taking a subset of the data, doing the calculations, moving on to the next subset of data?

Thank you for taking the time to fill in that you are using R14SP2, that will help us not waste time suggesting some of the functions added recently.

[michael]

The loop is on the matrix and vector generation. Each time, I'm taking only single sample of the data (i.e. x(i), y(i), z(i), phi(i),theta(i), psi(i))

PS, I'd be glad if you can also add some notes on the changes in latest releases.

[Bruno Luong]

"So far, I'm doing a for loop, which is not a Matlab way. "

Anything allowed by MATLAB IS MATLAB way.

Answer 1

[Bruno Luong]

% Test data
N = 4;
Phi     = 2*pi*rand(1,N);
Theta   = 2*pi*rand(1,N);
Psi     = 2*pi*rand(1,N);
X       = rand(1,N);
Y       = rand(1,N);
Z       = rand(1,N);

Phi     = reshape(Phi,      1, 1, []);
Theta   = reshape(Theta,    1, 1, []);
Psi     = reshape(Psi,      1, 1, []);
X       = reshape(X,        1, 1, []);
Y       = reshape(Y,        1, 1, []);
Z       = reshape(Z,        1, 1, []);
sB = sin(Phi);   cB = cos(Phi);
sD = sin(Theta); cD = cos(Theta);
sE = sin(Psi);   cE = cos(Psi);
T = [ cD.*cE, -cB.*sE+cE.*sB.*sD,  sB.*sE+cB.*sD.*cE;
      cD.*sE,  cB.*cE+sB.*sD.*sE, -cE.*sB+cB.*sD.*sE;
         -sD,             sB.*cD,             cB.*cD ];
XYZ = [X; Y; Z];
xyz = pagemtimes(T, XYZ)

xyz = 
xyz(:,:,1) =

    0.3128
    0.5127
   -0.3960


xyz(:,:,2) =

   -0.7072
   -0.7636
    0.1150


xyz(:,:,3) =

   -0.1876
    0.0750
    1.0194


xyz(:,:,4) =

    1.2058
   -0.6237
    0.2521

% For older MATLAB
%XYZ = [X, Y, Z];
%xyz = sum(T.*XYZ,2)

[michael]

Please note that I'm working with R14 while the pagemtimes is from R2020b

[Bruno Luong]

You'll mtimesx (and few others) from File Exchange that work similarly for older MATLAB versions.

[Bruno Luong]

Or you can do this:

XYZ = [X, Y, Z];
xyz = sum(T.*XYZ,2)