# How to use input string as a function in Appdesign?

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Abrar on 21 Feb 2023
Commented: Abrar on 21 Feb 2023
I am beginner in appdesigning. However, I am trying here to make an interface where user will write down the equation of a function and the value of the variable. After clicking the button,he will get the value of f(x) for the given value. Maybe I have some errors in the codes for which,after giving datas and clicking then,there seems something wrong. Someone please help me to debug this I need that emergency.

Simon Chan on 21 Feb 2023
Edited: Simon Chan on 21 Feb 2023
In case you would like to use function str2func, the string in the editfield for entering the equation should looks like the following:
@(x)x^2
x^2
and use the following inside the callback
f = str2func(s)
f = @(x)(str2func(s))
Abrar on 21 Feb 2023
Awwwww it worked. Thanks a loooot <3

### More Answers (1)

Steven Lord on 21 Feb 2023
If the user enters an expression in the edit field, you can convert it into an anonymous function using a couple of functions.
s = 'x^2+y';
Make it so it can be called with a vector of values using the vectorize function.
vecFunction = vectorize(s)
vecFunction = 'x.^2+y'
Get the list of variables using symvar.
vars = symvar(s)
vars = 2×1 cell array
{'x'} {'y'}
Assemble the string representation of the anonymous function, joining the list of variables and the function that was entered into the edit box.
str = "@(" + join(vars, ", ") + ") " + vecFunction
str = "@(x, y) x.^2+y"
Make the anonymous function with str2func.
f = str2func(str)
f = function_handle with value:
@(x,y)x.^2+y
To check let's call the function handle.
z = f(1:10, 100)
z = 1×10
101 104 109 116 125 136 149 164 181 200