I'm trying to simplify an expression or equation symbolically and I get the same error every time. Undefined function or variable 'x'.

I'm trying to simplify an expression symbolically and I get the same error every time.

Undefined function or variable 'x'.

I'm even using the actual example matlab provides. Trying to just simplify the expression sin(x)^2 + cos(x)^2 I get the error everytime. I'm brand new...what am I missing.

Answer 1

[Meghana Dinesh]

What exactly is your command? It seems like you haven't told MATLAB what the value of x is. First, initialize a value for x and the carry on.

 x = 0.5;
 sin(x)^2 + cos(x)^2;

[MichaelTee]

Wow I guess I'm trying to make it to complicated. I want to simplify a much more complicated expression to find some constants of integration and I was trying to stay away from that in order to solve them later. But I guess I can define them first and then go back and do some tinkering. I tried defining x as an integer first, but that still didn't work. Thanks for the quick response.

[MichaelTee]

Actually now I'm getting the error

undefined function 'simplify' for input arguments of type 'double'.

[MichaelTee]

I tried your code and it gives me a specific answer. I want to simplify an expression. Not get a specific answer.

[Walter Roberson]

simplify() requires the Symbolic Toolbox, and it works on symbolic expressions.

syms x
simplify( sin(x)^2 + cos(x)^2 )

Answer 2

[Bala Abhirami]

The function u[1]/(u[2]^0.5) shows the error "result of the function is undefined" in matlab simulink user defined function. What could be the reason?

[Walter Roberson]

Simulink uses MATLAB indexing syntax, so you need () instead of []

u(1)/(u(2)^0.5)

You might be able to use

u(1)/sqrt(u(2))