I'm trying to ad a condition to an equation

I'm trying to write an equation like

fx=@(x) sin(x)^2/x

But i need to add a condition to avoid a division by zero.

I've manage to do just that by writing a function but it seem to overcomplicate everything.

function [fx]=fv(x)
  if x == 0
    fx=x;
  else
    fx=sin(x)^2/x;
   end
end

Any idea would help me a lot.

Thanks

Answer 1

[David Goodmanson]

Hi Xavier,

I don't think your original function is overcomplicated at all. It's straightforward code that is self-commenting, which is very much in its favor. Even clearer would be

function fx = fv(x)
  if x == 0
    fx = 0;      <---
  else
    fx=sin(x)^2/x;
   end
end

Jesus Royeth's previous answer works well, but what if you ran up against this piece of code a few years from now?

fx=@(x) (x~=0)*sin(x)^2/(x+(x==0))

What is it up to? It needs a comment (I don't think Jesus is implying at all that it would not need one in working code):

fx = @(x) (x~=0)*sin(x)^2/(x+(x==0))     % impose fx(0) = 0

An important consideration is that the function only works for a single scalar input, and while that is okay, Matlab operates very much in a vector and matrix environment. Here is a version that uses ./ and .^ to allow element-by-element operations on vector input:

function fx = fv(x)
fx = sin(x).^2./x;
fx(x==0) = 0;
end

The idea here is than any instances of x = 0 produce 0/0 = NaN, and the second line takes care of those.

[Xavier Côté]

Thanks for the tips about the single scalar vs vector. I'm new to matlab and this one cause me a few problem.

Answer 2

[JESUS DAVID ARIZA ROYETH]

a trick:

fx=@(x) (x~=0)*sin(x)^2/(x+(x==0))

[Walter Roberson]

This does work to cleverly avoid the division by 0.

[JESUS DAVID ARIZA ROYETH]

thank you very much for your comment mr Walter Roberson.

[Xavier Côté]

Perfect. Clever simple. Exactly what I was looking for.

[darova]

Works without (x~=0) too