How to display a graph after getting user to input in the pop up?

Question:

A window should pop up that asks the user to input a single variable equation (a.k.a. function) for which the user wishes to find the root.

ii) A graph of this equation should get displayed

My code:

prompt = {'Single variable equation:                        \color{white} .'};
dlg_title = 'Input';
num_lines = 1;
defaultans = {'x'};
options.Interpreter='tex';
answer = inputdlg(prompt,dlg_title,num_lines,defaultans,options);
func = string(answer{1});

What to do next? New to MATLAB, please help.

[Rena Berman]

(Answers Dev) Restored edit

Answer 1

[Walter Roberson]

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

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

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

[oshawcole]

answer = inputdlg(prompt,dlg_title,num_lines,defaultans,options);
func = str2func(answer{1});
fplot(@(x) func)

still giving errors

[Walter Roberson]

func = answer{1};
f = str2func((['@(',char(symvar(func)),')', func]));
fplot(f)

[oshawcole]

How do I call x in the str2func syntax? it is not plotting the right graphs. for ex, the function fplot(@(x) func) was calling x.

[oshawcole]

when I add x.^2-4 in the prompt dialogue, it gives me wrong roots. it shows me a parabola passing through 0.

[Walter Roberson]

How do I know that you are not going to just delete your question after I answer it? When you delete your question after I have answered, you treat me as if I am a free private consultant. If you want a private consultation then you can hire a private consultant; if you want free advice then the price we charge is that your question and the responses must remain public for everyone to learn from.

[Walter Roberson]

The meaning of

   @(x) func

is the same as

@(x) func()

which means that a local variable named "x" is to be accepted on input, and then func() is to be called with no parameters.

The syntax

@(x) func(x)

would mean that a local variable named "x" is to be accepted on input, and then func() is to be called passing that variable as a parameter. @(x) func(x) means almost exactly the same thing as @func alone without the (x) part, except that using @(x) func(x) will only work if exactly one input is provided, whereas @func would work if multiple inputs are provided if func accepts multiple inputs.

In

f = str2func((['@(',char(symvar(func)),')', func]));

then notice the symvar(func) and at that point func is a character vector. symvar(func) looks through the string to figure out which variable the user used -- so for example if the user had entered 'sin(t).^2' then symvar would return the 't' . When symvar is used properly, the user is not restricted to using a particular variable name.

The above code constructs @(VARIABLENAME) CODE . In the 'sin(t).^2' example, @(t) sin(t).^2 would be constructed; if the user had coded 'besselj(1/2, x)' then @(x) besselj(1/2,x) would be constructed.