Passing a string to a function

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Jared
Jared 2013-11-20
评论： Sean de Wolski 2013-11-20
If I have a function:
function zp=F(x,z)
zp=zeros(2,1);
zp(1)=z(2);
zp(2)=a*sqrt(1+z(2)^2)+kx;
And I utilize it by:
[x,z]=ode45(@(x,z) F(x,z,a,kx),[x0,xf],[z10,z20]);
It works fine if I define a and kx equal to a number. However, in the case that a or kx may not equal a number, but another variable expression, I am not sure how to pass that. I tried kx='x^2', which doesn't work. But if I type x^2 in place of kx in the command line, it works. How can I set the kx equal to a variable epxression which can be passed to the function?

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回答（1 个）

Sean de Wolski
Sean de Wolski 2013-11-20
Just pass in x^2
[x,z]=ode45(@(x,z) F(x,z,a,x^2),[x0,xf],[z10,z20]);
It's throwing an error because inside of F you're trying to add a two element string. The anonymous function creation captures the workspace so you can have dynamic things (such as x^2) in it.
Also, your F function needs to take four inputs:
function zp=F(x,z,a,kx)
zp=zeros(2,1);
zp(1)=z(2);
zp(2)=a*sqrt(1+z(2)^2)+kx;
So that it can retrieve them from the anonymous function.
  2 个评论
Jared
Jared 2013-11-20
I got it to work as you state, by just putting in x^2. However, I have a bunch of different expressions, and I didn't want to have to call that whole expression each time, and instead, use a loop.
Sean de Wolski
Sean de Wolski 2013-11-20
Loop over the values calculated by the various expressions...

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