Assigning a placeholder variable

I am by no means a Matlab expert so I apologize if this is a question with an easy answer, but I couldn't find any help online.

I have y=x*exp(-(x^2))+x for all x

y is given by previous functions and is some real number

however,x is not yet defined, and I can't get the formula into x= form How can I input this formula without having x defined yet? Is there a way to define x as an empty value and then impute the formula, getting the actual value for x? What am I missing here?

EDIT: I got it to work using fzero. Now I am trying to rework the code to get it to work when y exists as a range of known values instead of one known value. It looks like fzero can't be vectorized, so I tried using a for loop. I get the results, but r0 gts printed into the command line for each value of rm. I want to create a vector of all of the r0 values (and then all of the x0,y0 values). Is this possible?

Here is the code I currently have:

mu=2
nsamples=100;
for rm=linspace(-2,2,10000)
funct=@(r0,rm)mu*r0.*exp(-r0.^2)+r0-rm
options=optimset('Display','off')
[r0]=fzero(@(r0) funct(r0,rm),-2)
end

[Sara]

Do you mean that you want to solve for x, given y? fzero can help you with that

[José-Luis]

By xexp did you mean x * exp?

[Daniel]

Ok, I got it to work using fzero. Now I am trying to rework the code to get it to work when y is a vector of known values, instead of one known value. It looks like fzero can't be vectorized. is there another way of of tackling this problem with a vector?

Answer 1

[José-Luis]

your_fun = @(x) x.*exp(-(x.^2) ) + x
your_fun(3)

Please accept the answer that best solves your problem.

[Daniel]

This works if I set the x value after the fact (as in your example). I have a known y value, so I just had to use the fsolve function. See above for the problem I'm having with the for loop/not being able to vectorize the fsolve function

[Image Analyst]

You forgot to attach your updated code.

[Daniel]

updated code:

mu=2
nsamples=100;
for rm=linspace(-2,2,10000)
funct=@(r0,rm)mu*r0.*exp(-r0.^2)+r0-rm
options=optimset('Display','off')
[r0]=fzero(@(r0) funct(r0,rm),-2)
end

Also see above

Answer 2

[Elias Hasle]

Couldn't you use the symbolic toolbox? E.g.:

syms x_symbol
y = <some expression of x_symbol>
z = <some other expression of x_symbol, could include the y expression etc.>
x_value = 1234
z_result = double(subs(z, x, x_value))