Error Inner Matrix Dimensions must agree?? Help!
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So i am trying to solve for these 2 values but i keep getting an error aobut my matrix dimensions. i dont know why, i will attach what my x value is.
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Error using * Inner matrix dimensions must agree.
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ang_position=x(:,1);
ang_velocity=x(:,2);
ang_accel= diff(ang_velocity);
a_cmx= (ang_accel.*(L./2).*cos(ang_position))-((ang_velocity.^2)*(L/2)*sin(ang_position));
a_cmy= (-ang_accel.*(L./2).*sin(ang_position))-((ang_velocity.^2)*(L/2)*cos(ang_position));
采纳的回答
Geoff Hayes
2014-7-29
Suppose x is of dimension nx2. Then from
ang_position=x(:,1);
ang_velocity=x(:,2);
both of these vectors are of dimension nx1.
Now check the next line of code
ang_accel= diff(ang_velocity);
The above creates ang_accel which is of dimension (n-1)x1 because of diff reducing the length of the input vector by one. This creates the error at the line
(ang_accel.*(L./2).*cos(ang_position))
because the two vectors, ang_accel and ang_position, are of different dimensions. You may just want to replace
ang_accel= diff(ang_velocity);
with
ang_accel= [0 ; diff(ang_velocity)];
so that the dimensions are correct (and zero seems valid, since there is no prior data to determine the acceleration for the first element).
Note also that you will have to update your final two lines of code so that the pair-wise multiplication can occur for all cases (missing from the final multiplication of each line)
a_cmx= ((ang_accel*(L/2)).*cos(ang_position))-(((ang_velocity.^2)*(L/2)).*sin(ang_position));
a_cmy= ((-ang_accel*(L/2)).*sin(ang_position))-(((ang_velocity.^2)*(L/2)).*cos(ang_position));
Note that for scalar multiplication, the period is not needed: I replaced
ang_accel.*(L./2)
with just
(ang_accel*(L/2))
更多回答（1 个）
Azzi Abdelmalek
2014-7-29
A=1:5
B=diff(A)
Notice that A and B haven't the same size
2 个评论
Azzi Abdelmalek
2014-7-29
编辑：Azzi Abdelmalek
2014-7-29
You should reduce the size of all your initial array, even L if it's an array. There are also errors in your code
If L is an array, use L(1:end-1)
x=rand(10,2);
ang_position=x(:,1);
ang_velocity=x(:,2);
ang_accel= diff(ang_velocity);
ang_position1=ang_position(1:end-1)
ang_velocity1=ang_velocity(1:end-1)
a_cmx= (ang_accel.*(L./2).*cos(ang_position1))-((ang_velocity1.^2).*(L/2).*sin(ang_position1));
a_cmy= (-ang_accel.*(L./2).*sin(ang_position1))-((ang_velocity1.^2).*(L/2).*cos(ang_position1));
David
2014-7-29
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