Passing a string to a function

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Jared 2013-11-20

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https://ww2.mathworks.cn/matlabcentral/answers/106985-passing-a-string-to-a-function

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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Answer 1

Sean de Wolski 2013-11-20

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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.

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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.