How to rewrite a non-linear function so that f(x) = 0?

Hello! This is my first question on these forums, so please forgive me if I do anything wrong here :). What I wonder about is how to make MATLAB rewrite a general, non-linear function. Say that I input the function "3cos(x) = x^2" or "e^x = 2x". Is there any function for this? What I want to do with this new, rewritten function is to use it to find the point of zero. This I plan to do with a function of my own, instead of using fzero. Thank you all in advance!

Answer 1

[Walter Roberson]

You would have to input the equation as a string. Search for the '=' in the string, insert a '(' immediately after that and a ')' at the end, and convert the '=' to '-'. The result will be an expression with an implicit "= 0"

After that you have to figure out how to do calculations based upon a string. For that, please see http://www.mathworks.com/matlabcentral/answers/22330-can-you-have-the-user-input-an-equation-in-matlab

Answer 2

[Honglei Chen]

Isn't it just

3*cos(x)-x^2

and

exp(x)-2*x

If you have to, you can define function f1(x) for the left side and f2(x) for the other side and then use f1(x)-f2(x). But IMHO it really doesn't save you anything.

Answer 3

[Christian Skoog]

I want MATLAB to do exact that calculation, yes. How do I write the code so that it does that?

Answer 4

[Sean de Wolski]

If you have the Symbolic Math Toolbox, you can just use solve()

solve('exp(x)=2*x')
solve('3*cos(x)=x^2')

doc solve

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MORE

syms x
f1 = x^2-3
f2 = cos(x*exp(x))
simple(f2-f1)

Answer 5

[Christian Skoog]

No, I don't want the solution to the calculation. I want MATLAB to be able to rewrite the calculation. I want MATLAB to be able to transform 3*cos(x)=x^2 to 3*cos(x)-x^2=0, and e^x=2*x to e^x-2*x=0. The user would call a function that calculates the point of zero, by inputting a non-linear function and a starting guess. For this I need to be able to rewrite a general non-linear function to one with only 0 to the right of the "equals to" or = sign. How would I go around doing this? "...you can define function f1(x) for the left side and f2(x) for the other side and then use f1(x)-f2(x)" This sounds like a quite good idea. How would I do this when the function would be input for a function within MATLAB?