MATLAB: This is happening

image processing

[m n] = size(image);

I tried this command earlier and it worked well but now showing this:

"Indexing cannot yield multiple results."

Did you name one of your variables ‘size’ later in your code?

The definition of characteristic polynomial seems to vary. For example, Wolfram World defines it the way you did, but Wikipedia would define it as

Pcaratt = det(lambda*I-M);

Then you would get Pcaratt=polinomio. Either way, the equations have the same roots, so the choice of sign is not very important.

Use

 alpha = str2num(answer{1})

instead. answer{1} is a string that needs to be converted first.