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Error with matrix calculation

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Tobias
Tobias am 2 Mai 2024
Kommentiert: Tobias am 3 Mai 2024
% matrix calculation
M3 = [0 0 0 0 -1 0 0 0 0 0 1 0;
0 0 0 0 0 1 0 0 0 0 0 0;
0 0 0 0 0 0 0 0 0 0 -0.05 1;
1 0 0 0 0 0 0 0 -1 0 -1 0;
0 -1 0 0 0 0 0 0 0 -1 0 0;
-0.15 0 0 0 0 0 0 0 -0.15 0 0.05 0;
-1 0 1 0 0 0 0 0 0 0 0 0;
0 1 0 1 0 0 0 0 0 0 0 0;
-0.4*sind(20) -0.4*cosd(20) -0.4*sind(20) 0.4*cosd(20) 0 0 0 0 0 0 0 0;
0 0 0 -1 0 0 0 1 0 0 0 0;
0 0 (BD/2)*cosd(Angle_FBD) (BD/2)*sind(Angle_FBD) 0 0 (BD/2)*cosd(Angle_FBD) (BD/2)*sind(Angle_FBD) 0 0 0 0];
N3 = [mass_body1*Acceleration_G1x;
mass_body1*Acceleration_G1y+mass_body1*9.81;
mass_body1*radius_body1^2*alpha_1;
mass_body2*Acceleration_G2x;
mass_body2*Acceleration_G2y+mass_body2*9.81;
(1/12)*mass_body2*radius_body2^2*alpha_2;
mass_body3*Acceleration_G3x;
mass_body3*Acceleration_G3y+mass_body3*9.81;
(1/12)*mass_body3*radius_body3^2*alpha_3;
mass_body4*Acceleration_G4x;
mass_body4*Acceleration_G4y+mass_body4*9.81;
(1/12)*mass_body4*BD^2*alpha_4];
X = M3/N3
It says that there is an error using "/" and that matrix dimensions must agree. I dont know exactly what this means, and can't find where the issue is. The error is in the line "X = M3/N3"
  4 Kommentare
Tobias
Tobias am 3 Mai 2024
M3 is A and N3 is B
Tobias
Tobias am 3 Mai 2024
I forgot a row with values in M3, but it still doesnt work. M3 is now 12 12, and N3 is 12 1

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Antworten (2)

James Tursa
James Tursa am 2 Mai 2024
We don't have all the variables necessary to run your code, but guessing that maybe you need element-wise divide instead of matrix divide?
X = M3 ./ N3
Note the period, so try ./ instead of just /

Walter Roberson
Walter Roberson am 3 Mai 2024
When you use the / (matrix right divide) operator, the two operands must have the same number of columns. The resulting matrix will have a size that is the number of rows of the first operand, by the number of rows of the second operand.
A = rand(5,3); B = rand(7,3);
A / B
ans = 5x7
0 0 0 0 1.8427 1.2240 -0.1906 0 0 0 0 -0.3170 0.8279 0.7349 0 0 0 0 1.1372 0.7934 0.5501 0 0 0 0 0.2419 1.0085 -0.2503 0 0 0 0 0.2136 1.2041 -0.0009
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You appear to be constructing an 11 x 12 matrix and dividing it by a 12 x 1 matrix. None of the operators \ .\ / or ./ would be suitable for that purpose.
It would not be an error to calculate
X = M3/N3'
which would then be an 11 x 12 matrix divided by a 1 x 12 matrix, which would give an 11 x 1 result.

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