Subscript indices must either be real positive integers or logicals?

Hello, I'm trying to define the Sherman-Morrison formula:

using the code

invA = A.^(-1)

n=size(A,1)

u=ones(n,1)

Z = 1 + u'*invA*u

inv(A + u*u')=invA - 1/Z * invA * u*u' * invA.

I'm using Z here instead of alpha in the problem. It always returns to an error "Subscript indices must either be real positive integers or logicals". What does it mean? Can somebody help with it??

Matlab new starter here, all help would be appreciated. Thanks heaps!!

Answer 1

[Ahmet Cecen]

There is a more fundamental issue here:

inv(A + u*u')=invA - 1/Z * invA * u*u' * invA

The above line indicates that you need to go over some basic MATLAB tutorials. You can't just type and equation with variables on both sides and solve it like you would in Maple or Mathematica. While:

New = inv(A + u*u')

is a perfectly valid line:

inv(A + u*u') = New

is not.

Answer 2

[Image Analyst]

People ask about this all the time and so there is a FAQ entry for it.

The error is well explained in the FAQ: http://matlab.wikia.com/wiki/FAQ#How_do_I_fix_the_error_.22Subscript_indices_must_either_be_real_positive_integers_or_logicals..22.3F

Answer 3

[Image Analyst]

This is not proper syntax:

inv(A + u*u') = invA - 1/Z * invA * u*u' * invA

You can't have operations on the left hand side of an equals sign. It can only be a variable that you want to send the right hand side into.