Trying to create a callback function on App Designer.

Hello,

I can be considered as newbie for Matlab and am trying to create an application that calculates the nominal interest rate "i".

i = N*((T/P)^(1/(N*Y))) - N where

i = nominal interest rate

P = initial investment

T = future value

N = number of compounding periods per year

Y = number of years

The basic look of my application as following:

I want this application to execute the function that I gave above when you click the calculate button. In order to to that, I right click the calculate button and after that click callback then add the function up there. However, I do not know how to display it on the bottom field and I get an error when I click the calculate button as following, you can also see my callback function there:

As a result, what is my mistake and what should I do to create this callback function properly and display its result on the "i" field?

Appreciated for your help.