sym error in define functions

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Rastgo Mhamad
Rastgo Mhamad 2021-3-4
评论： Walter Roberson 2021-3-4
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.....

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采纳的回答

Steven Lord
Steven Lord 2021-3-4
Ran in:
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 = 
  2 个评论
Walter Roberson
Walter Roberson 2021-3-4
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.)

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