isolate a variable?

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Artur M. G. Lourenço
I can isolate one variable as an expression? example:
'x^2+2+x' em 'x = x^2 +2'
remembering that they are symbolic objects.
Thanks in advance.

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Walter Roberson
Walter Roberson 2011-9-2
If your input is x^2 + 2 + x then you cannot isolate x to one side of an equation, as your input is not an equation.
If your input is implicitly x^2 + 2 + x = 0 then your example output of x = x^2 + 2 is incorrect: instead x = -x^2 - 2
You cannot always isolate one variable -- not unless you are willing to make some restrictions on the form of the equation.
If you have a polynomial as input, then
S = x^2+2+x;
c = sym2poly(S);
isolated_x = x * c(end-1) - S;
  2 个评论
Artur M. G. Lourenço
Artur M. G. Lourenço 2011-9-2
Thank you and sorry for having written the equation the wrong way. However I could not do the same for this equation:
f = x * pi * sqrt (x ^ 2 +20 ^ 2);
it is possible to do in the Symbolic Math Toolbox?
Walter Roberson
Walter Roberson 2011-9-2
Usually what you do is solve() for a variable, rather than try to isolate the variable.
You could try working with map() and coeff(), but as I do not have the Symbolic Toolbox I am not certain what result you will get for terms that do not have the variable. The coeff() page indicates that FAIL should be returned; I do not know what FAIL translates to when moved from the MuPad side to the MATLAB side.

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