Can you have the user input an equation in MATLAB?

I know I've been posting quite a few questions here but my MATLAB final is due in several days and I'm trying to make sure my program is going to be good. IO'm just wondering if it's possible for a user to input an equation? For example in the volume calculator I am working on I would like to have the user define a set of variables and then input an equation consisting of those variables and of course have matlab solve the equation. If this is possible what would be the code? I have snooped around online for a bit and have not found it.

Answer 1

[Daniel Shub]

There are a number of ways of doing this ... I think they all involve eval, which makes them problematic. Assuming you have a string str with the function that you want to evaluate, the simplest, but worst answer is:

x = eval(str);

I think I would do something like:

f = function_handle.empty; % I think this helps mlint with the eval
f = eval(['@()', str]);
x = f(); % Note the () is important

This limits the problems that the eval can cause.

Answer 2

[Walter Roberson]

A couple of alternate formations are shown at http://www.mathworks.com/matlabcentral/answers/15450-convert-a-symbolic-equation-to-a-vector-equation

If you have a new enough version, an explicit eval is not needed to create an anonymous function.

Some people use the older inline() instead of an anonymous function.

Equations can also be evaluated by using the facilities of the symbolic toolbox.

[Daniel Shub]

I cannot get inline or str2func to work for the case where "the user defines a set of variables". I take this to mean something like: x = 1; y = 2; and you want f = x+y = 3.

Answer 3

[lbon jbn]

Awesome, thank you guys, I got it to work!