Help with symbolic substitution

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Richard Fiifi Annan
评论： Richard Fiifi Annan 2021-7-27
I have created zz that has 3 symbols, x_1, x_2 and x_3. I later generated 3 random numbers, xx, to replace the symbols and calculate zz.
My problem now is how to substitute the 3 random numbers such that the 1st, 2nd and 3rd numbers respectively replace x_1, x_2 and x_3 in order to calculate a value for zz as pp.
%
syms x_1 x_2 x_3
y = (x_1 + x_2 + x_3)^2;
yy = expand(y)
numerator = (x_1*x_1) + (x_1*x_2) + (x_1*x_3);
zz = numerator / yy
% Generate a random number for each of x_1, x_2 and x_3:
xx = randi(10,[1 3]);
% Use xx to calculate zz:
pp = subs(zz, xx) % ouput is incorrect. Help is needed!

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采纳的回答

Yongjian Feng
Yongjian Feng 2021-7-27
%
syms x_1 x_2 x_3
y = (x_1 + x_2 + x_3)^2;
yy = expand(y)
numerator = (x_1*x_1) + (x_1*x_2) + (x_1*x_3);
zz = numerator / yy
% Generate a random number for each of x_1, x_2 and x_3:
x_1=randi(10);
x_2=randi(10);
x_3=randi(10);
pp = subs(zz)

更多回答（1 个）

KSSV
KSSV 2021-7-27
Ran in:
Why don't you use anonymous function ?
zz = @(x) (x(1) + x(2) + x(3))^2/(x(1)^2 + x(1)*x(2) + x(1)*x(3)) ;
% Generate a random number for each of x_1, x_2 and x_3:
xx = randi(10,[1 3]);
% Use xx to calculate zz:
pp = zz(xx)
pp = 1.2857
  1 个评论
Richard Fiifi Annan
Richard Fiifi Annan 2021-7-27
Thanks for the quick response @KSSV. Surely your answer solves the problem. My reason for posting the question was because zz is a product of some other calculations upstream. So I thought perhaps there might be an MATLAB in-built function for solving it.

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