Error in multipying a 3 by 3 matrix with a 3 by 1

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Xa = app.previewTABLE.Data(:,1);
Ya = app.previewTABLE.Data(:,2);
Za = app.previewTABLE.Data(:,3);
B = [DifX;DifY;DifZ];
C = [Xa;Ya;Za]; %% 3x1 matrix
Ri = [Sci Rz -Ry;-Rz Sci Rx;Ry -Rx Sci]; %%3x3 matrix
R = C * Ri
%%% This is the error am getting for trying to multiply a 3x3 matrix by a 3x1 (C * Ri).
Error using *
Incorrect dimensions for matrix multiplication. Check that the number of columns in the first matrix matches the number of rows in the second matrix. To perform elementwise multiplication, use '.*'.

Answers (2)

Alan Stevens
Alan Stevens on 11 Aug 2021
Check that the number of columns in the first matrix matches the number of rows in the second matrix.
Ri has 3 columns, C has 3 rows, so Ri*C will work, but with C having 1 column and R having 3 rows, C*Ri will not!
  1 Comment
Joshua Naah
Joshua Naah on 11 Aug 2021
Yh I just tried that and it didn't work. I should mention that am working in app designer, so when I first got the error I tried the same code in the command window and it worked just fine so am a bit surprised getting an error with the same code in app designer.

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Steven Lord
Steven Lord on 16 Feb 2024
Xa = app.previewTABLE.Data(:,1);
Ya = app.previewTABLE.Data(:,2);
Za = app.previewTABLE.Data(:,3);
C = [Xa;Ya;Za]; %% 3x1 matrix
Is this a 3-by-1 matrix? What size is app.previewTABLE.Data? If it is an m-by-n array, each of Xa, Ya, and Za will have m rows and C will be (3*m)-by-1 (unless app.previewTABLE.Data is a table array whose variables themselves have multiple columns.) That's only 3-by-1 if m is 1 (meaning app.previewTABLE.Data is a row vector.) From the name I suspect that it's not a row vector and so C isn't 3-by-1.
Ri = [Sci Rz -Ry;-Rz Sci Rx;Ry -Rx Sci]; %%3x3 matrix
You didn't show the definition of any of the variables you use here, so it's impossible to say that Ri is a 3-by-3 matrix. Let's say, for example, that each of Sci, Rz, Ry, and Rz were 2-by-2 matrices. This concatenation would be defined and would result in a 6-by-6 matrix not a 3-by-3.

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