Inner matrix dimensions must agree.

Hi, having a little trouble making it multiply.

Sorry but I am fairly new to the software, and so have probably missed something very basic.

 function move(n)
  %column 1 is x, 2 is y, 3 is velocity, 4 is angle (radians)
  P=10*rand(n,4);

plot(P(1:10,1),P(1:10,2),'o')

for t=0:0.01:20

      P=P+(P(1:n,3)*(P(1:n,1)*cos(P(1:n,4))+P(1:n,2)*sin(P(1:n,4))));

      plot(P(1:10,1),P(1:10,2),'o')
      pause(0.5);
  end

Any help would be great.

Answer 1

[Ganesh Gaonkar]

From your question, It was not clear to me, what value of 'n' you are passing to this function. However, you can just put a break point in the line above the one where the error occurs to see if all arguments/variables are getting calculated with right dimensions.That way you can check the value of each variables in debug mode and locate the cause of the issue.

Answer 2

[dpb]

   P=P+(P(1:n,3)*(P(1:n,1)*...

'*' is matrix multiply in Matlab and P(1:n,N) is a column vector of size nx1. To multiply two it would have to be nx1 X 1xn or 1xn X nx1 depending on whether you intend the result to be n-by-n or 1-by-1.

Or, if you intend the result to be the element-wise product of the two vectors and the result to be nx1 then

doc times

for the "dot" operator.