CODEWITHSUNDEEP
matlab
llinfeng
llinfeng

Reputation: 49

Error: ()-indexing must appear last in an index expression

I am trying to evaluate the following expression:

 (-a(3)*(4*b(1,1)*b(2,2)-b(1,2)*b(2,1))+b(3,2)*(2*b(1,1)*a(2)+b(1,2)*b(2,1)))/(2*b(3,3)*(4*b(1,1)*b(2,2)-b(1,2)*b(2,l,1))-b(3,2)(2*b(1,1)*b(2,3)-b(1,2)*b(2,1)))

It is for expression (in latex):

$\left(\frac{-a_3 (4\beta_{11}\beta_{22}-\beta_{12}\beta_{21} ) +\beta_{32}(2\beta_{11}a_2+\beta_{12}\beta_{21})}
      {2\beta_{33} (4\beta_{11}\beta_{22}-\beta_{12}\beta_{21} ) -\beta_{32}(2\beta_{11}\beta_{23} - \beta_{12}\beta_{21})}\right)$

Matlab keeps complaining that:

Error: ()-indexing must appear last in an index expression.

I want to check if I have the simplification right and would need such expression to be evaluated.

Upvotes: 2

Views: 1583

Answers (2)

Mohsen Nosratinia
Mohsen Nosratinia

Reputation: 9864

You have to add an asterisk after b(3,2). Currently the term that starts with b(3,2) is like this:

b(3,2)(2*b(1,1)*b(2,3)-b(1,2)*b(2,1))

You should change it to

b(3,2)*(2*b(1,1)*b(2,3)-b(1,2)*b(2,1))

The problem is that Matlab interprets that as indexing b(3,2) which is already an indexed expression.

Upvotes: 3

Ben Voigt
Ben Voigt

Reputation: 283624

It looks like your matrix b is two-dimensional, but your expression contains b(2,l,1) which has three subscripts.

The original formula didn't have any l in it.

enter image description here

Upvotes: 2

Related Questions