Defining a symbolic function in which one of the arguments is used to look up an entry of a vector, which is then used in the function.

Question

Robert Mason 2016-7-20

0
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https://ww2.mathworks.cn/matlabcentral/answers/296561-defining-a-symbolic-function-in-which-one-of-the-arguments-is-used-to-look-up-an-entry-of-a-vector

回答： Star Strider 2016-7-20

I have defined several numbers and a vector as follows:

d1=-0.3;d2=0.4;
dv=[d1 d2];

I now attempt to define a function in which one of the arguments of the function is used to look up an entry of the vector dv; and the selected entry of the vector is then used in the function. I have defined this function as follows:

syms y z
THETA(y, z) = dv(y) + z

I then want to use the function in a for loop (:

for j=1:MB;
Nzero(j, a)=sqrt((1/conj(a) - dv(j))*(THETA(l, a) - dv(j))/((a - dv(j))*(THETA(l, 1/conj(a)) - dv(j))));
end;

The issue that I am having is that MATLAB halts at

THETA(y, z) = dv(y) + z

Have I defined this function in an appropriate way for my use? In particular, I think the problem is with the use of the object dv(y) in this function. Is there a better way to code for one of the function's arguments to be used to look up an entry of a vector, which is subsequently used in the function?