sym error in define functions

when i define function by sym , exmp:

 f = sym('4*xˆ3+4*xˆ2-7*x+2'); 

it show me this

Error using sym>convertChar (line 1448)

Character vectors and strings in the first argument can only specify a variable or number. To

evaluate character vectors and strings representing symbolic expressions, use 'str2sym'.

Error in sym>tomupad (line 1214)

S = convertChar(x);

Error in sym (line 211)

S.s = tomupad(x);

what is the solution. thanks.....

Answer 1

[Steven Lord]

As the error message states, "To evaluate character vectors and strings representing symbolic expressions, use 'str2sym'."

So use str2sym. Alternately define x to be a symbolic variable then build the symbolic expression using it.

syms x
y = x.^2 + 2*x -3

y = 

[Rastgo Mhamad]

thank you so much.

[Walter Roberson]

Using sym('4*xˆ3+4*xˆ2-7*x+2') was permitted before R2018a if I recall correctly (might have been R2018a that was the last release.)