Matrix dimensions must agree.

This error usually occurs when you are trying to perform an operation on two matrices or vectors with incompatible dimensions. For example, if you try to add two matrices with different dimensions, you will get this error.

To fix this error, you need to ensure that the dimensions of the matrices or vectors involved in the operation are compatible. For addition and subtraction, the matrices must have the same number of rows and columns. For matrix multiplication, the number of columns in the first matrix must be equal to the number of rows in the second matrix.

If you are still having trouble, you can try printing out the dimensions of the matrices or vectors involved in the operation and checking if they are compatible.