Help plotting user input functions for Matlab App.

Hi all,

I have a project where I am trying to build an app which can plot simple user functions (such as quadratic, trignometric etc). I have an edit field text where the users will be able to add thier functions in. I want it so users do not have to include 'y =' into their function, but can rather type the components with x in it. eg. they could type 2x and that would be 'y=2x' or '5x^2 + 3' would be 'y=5x^2 + 3'. I have used the callback function and included the code within:

function EnterFunctionEditFieldValueChanged(app, event)
    value = app.EnterFunctionEditField.Value;
    x = -10:0.1:10;
    y = value;
    plot (app.UIAxes, x, y);
end

Now I am aware that the issue is probably with the 'y=value;' bit, but I really don't know any way to move foreward. The error message I get is 'Error using plot Invalid color or line style'. It is to be noted that when I only insert x into the textbox, I do get a function (with error lines I believe). See below: All help is appriciated.

Answer 1

[Voss]

The reason using 'x' works is because 'x' is a valid line marker, so MATLAB plots x = -10:0.1:10 against its indices, 1:201 (note the X-axis values) using the marker 'x' (i.e., each point is plotted with an 'x' marker).

To get it to work properly for any function of x, you can make the user-input into a function using str2func and evaluate that function at your specified x values (-10:0.1:10):

ax = gca(); % an axes to plot into

x = -10:0.1:10; % fixed x values to plot over

value = 'x'; % user input

y = str2func(['@(x)' value]) % y is the anonymous function @(x)x

y = function_handle with value:
    @(x)x

plot(ax, x, y(x)); % evaluate y at x and plot

value = 'x.^2'; % different user input

y = str2func(['@(x)' value]) % y is the anonymous function @(x)x.^2

y = function_handle with value:
    @(x)x.^2

plot(ax, x, y(x)); % evaluate y at x and plot