convert string to equation

Hi guys I am building an application using the app designer. However, I have ran into issue because I want the user to feed his equation into the app. However, the edited field can either be numaric or text so if fore example user want to input an equation (5*x^2) how would that be done? I have tried using string field and use str2double and str2num but that didn't work any thoughts on that?

[Stephen23]

Most likely one of these:

https://www.mathworks.com/help/matlab/ref/str2func.html

https://www.mathworks.com/help/symbolic/str2sym.html

Answer 1

[per isakson]

Or a smelling solution if you don't have the symbolic toolbox

>> x=3;
>> v = eval('(5*x^2)')
v =
    45
>> 

Create an anonymous function

>> foo = eval(['@(x)','(5*x^2)'])
foo =
  function_handle with value:
    @(x)(5*x^2)
>> foo(2)
ans =
    20
>> 

[Stephen23]

str = '5*x^2';
foo = str2func(sprintf('@(x)%s',str));
foo(2)

ans = 20

[per isakson]

That´s better!