Solve an expression including a function
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Is it possible to use "solve" for an expression including a function? E.g. solve('expression=f(function(x)))','x') Thanks
回答（2 个）
Oleg Komarov
2012-8-5
Bring everything to LHS:
solve('expression - f(function(x))','x')
1 个评论
Walter Roberson
2012-8-5
And note that in order to get anything useful out of this, the function would have to have been defined in the symbolic toolbox. You might find it easier to work with
solve(expression - f(function(x)), x)
(but of course "function" is a reserved word so you could not use that as the name.)
Star Strider
2012-8-5
In 2012a, this:
syms a b c x y f(x) g(x)
f(x) = sin(x) + cos(x)
g(x) = x / (x^2 + 1)
soln = solve( g(x) == f(x), x)
yields:
soln =
-226.98318440505298644743940820481
Since I was also curious to see if this sort of syntax worked.
Substituting:
g(x) = exp(y)
soln = solve( g(x) == f(x), x)
yields:
soln =
-log(exp(y)*(1/2 + i/2) + (2^(1/2)*(exp(2*y)*i - 2*i)^(1/2))/2)*i
-log(exp(y)*(1/2 + i/2) - (2^(1/2)*(exp(2*y)*i - 2*i)^(1/2))/2)*i
to be sure that it also can return symbolic solutions. It also works using only the expressions, without the function syntax.
(I made these functions up for this illustration. To the best of my knowledge they have no practical application.)
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2012-8-5
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