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In symbolic expression how to include an expression that is a function of the symbolic variable?

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László Arany
László Arany 2014-4-14
评论： Mischa Kim 2014-4-14
I have an expression given as e.g.:
g = @(x) f*x
where f is a function of x and is defined as
f(x) = b if x > a
f(x) = c if x <= a
and a,b,c are constant numbers.
1. How to define this function? How can a parameter depend on the symbolic variable in a symbolic expression?
2. How can I multiply two expressions like this? What I want to get is:
g = @(x) a*x;
h = @(x) b*x;
gh = g*h; % I want to get gh = a*b*x^2;
It gives an error saying
"Undefined function 'mtimes' for input arguments of type 'function_handle'."
I also tried gh = @(f) g*h, which also doesn't work.

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Mischa Kim
Mischa Kim 2014-4-14
编辑：Mischa Kim 2014-4-14
László, try
g = @(x) x*(c*(x<=a) + b*(x>a));
and
gh = @(x) g(x)*h(x);
  2 个评论
László Arany
László Arany 2014-4-14
Thank you, these work nicely and the first one is very elegant!
However, what if I have a more complicated function? Say I have to solve the dispersion relation inside the symbolic expression?
H = @(f) k*f;
where k = k(f) and it results from the nonlinear expression f^2 = k*g*tanh(k*S) with g=9.81; S=21? Can I solve this more complicated nonlinear equation inside a symbolic expression somehow?
Mischa Kim
Mischa Kim 2014-4-14
I believe this one is similar to the other question I just answered, unless you mean something different by solve...

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