Square of Objective function expression gives an error

Hi experts, I have just started doing optimization in the problem-based workflow. I refer to this documentation page, in order to formulate my own Non-Linear Objective function.

But when I run the following code,

obj = sum(residual.^2);

It produces the following error.

Undefined operator '.^' for input arguments of type 'optim.problemdef.OptimizationExpression'.

I am using MATLAB R2018a. My actual objective function expression is a bit complicated and I need to understand this error before I proceed further.

Your help will be highly appreciated. Thanks in advance!

[Walter Roberson]

The abilities of problem based optimization expanded in R2018b, you might be using too old of a version.

[pradeep kumar]

@ Walter Roberson, Thank you for your response. I will check that out in R2018b.