CODEWITHSUNDEEP
inputoctave
pizza lover
pizza lover

Reputation: 11

How to read function from keyboard in Octave and use it later?

I'm writing a script in Octave to calculate how will a ball bounce on a surface. But the surface is defined by a function that I have to read from user Input. I have a line:

funcInput = input("f(x,y) = ", "s")

that take what I write in terminal and save it as string to 'funcInput' variable. So far so good.
Now I need to substitute 'x' and 'y' in this function with other variables I have in this script, and then calculate roots of this function. And I have no idea how to do it...

Later I want to draw a surface so:

ezsurf(strcat('@(x, y) ', funcInput))

It produces an error

error: isinf: not defined for function handle

I guess this function does not take string as argument, cause when I do this:

ezsurf(@(x, y) (x.^2+y.^2)/10')

it works like a charm. So my question is: how can I make it work or what other way can I read function from user and use it later?

Upvotes: 1

Views: 350

Answers (2)

Tasos Papastylianou
Tasos Papastylianou

Reputation: 22225

Octave provides the str2func function for exactly this purpose.
(and also the inline function which is similar, but this is headed for deprecation)

E.g.:

funcInput = input("f(x,y) = ", "s")
f = str2func( strcat( '@(x, y) ', funcInput ) )
ezsurf( f, [ -10, 10 ] )

Having said that, ezsurf can indeed work directly from funcInput. What you're doing wrong is that you're trying to convert it to a string that looks like an anonymous function. Don't, just plug the string directly:

funcInput = input("f(x,y) = ", "s")
ezsurf( funcInput, [ -10, 10 ] )

Upvotes: 1

Avi
Avi

Reputation: 362

You can do it using the eval method:

funcInput = input('f(x, y) = ', 's');
eval(['func = @(x, y) (' funcInput ');']);
% Now the variable func is a function handle to the input function from the user

For example:

>> funcInput = input('f(x, y) = ', 's');
f(x, y) = x+4*y^2-2*x*y % user input
>> eval(['func = @(x, y) (' funcInput ');']);
>> func
func =

@(x, y) (x + 4 * y ^ 2 - 2 * x * y)

>> func(2, 3)
ans = 26

Hope it will be useful!

Upvotes: 1

Related Questions