How can I get a calculated function value???

Question

연승 김 2021-1-14

0
链接

此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/717138-how-can-i-get-a-calculated-function-value

评论： 연승 김 2021-1-27

I want to calculate Lagrangian fuction.

L(x_wt11, x_wt21, x_wt12, x_wt22) = Vt1 * ( (1-p_wt11)^x_wt11 * (1-p_wt21)^x_wt21 )...
    + Vt2 * ( (1-p_wt12)^x_wt12 * (1-p_wt22)^x_wt22 )...
    - lambda1 * ( 1-(x_wt11 + x_wt12))...
    - lambda2 * ( 1-(x_wt21 + x_wt22))...
    - lambda3 * ( Vw1 * (1-s_wt11/u)^x_wt11 * (1-s_wt12/v)^x_wt12...
                  + Vw2 * (1-s_wt21/u)^x_wt21 * (1-s_wt22/v)^x_wt22 - 2 * beta);

When I input L(0,0,0,0) (or L(1,0,0,0), L(0,1,1,0)...etc)

the answer is not calculated value, although I declare all parameters.

In this equation, "x_wt11, x_wt21, x_wt12, x_wt22" are binary variable,

and anothers are parameters(constant).

I declare parameters before this equation except 'u, v'

because 'u,v' are dependent on "x_wt11, x_wt21, x_wt12, x_wt22" value.

In summary,

1. declare parameters. (except 'u,v')

2. declare Lagrangian function.

3. declare parameters 'u, v'

* The reason why I declaring 'u,v' afterwards, I want to prevent deviding by zero.

* u = x_wt11 + x_wt21 , v = x_wt12 + x_wt22

* So, if "x_wt11=0", "x_wt21=0", and then u is zero.

* To solve this problem, I use "if" statement.

if (x_wt11+x_wt21) == 0
    u=1;
elseif (x_wt11+x_wt21) == 1
    u=1;
elseif (x_wt11+x_wt21) == 2
    u=2;
else 
    u=0;
end

And then, if I input "L(0,0,0,0)"

the answer is like this way, "52/(22*u) + 69/(22*v) + 74/56"

I declare parameters 'u,v' but, Why the answer is not a calculated??? and How I can solve this problem???

0 个评论
显示 -2更早的评论隐藏 -2更早的评论

请先登录，再进行评论。

请先登录，再回答此问题。

Answer 1

Steven Lord 2021-1-26

1
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/717138-how-can-i-get-a-calculated-function-value#answer_606658

在 MATLAB Online 中打开

Since you're mentioning that you evaluate the function and then define a value for u, I assume you're using symbolic variables from Symbolic Math Toolbox. Let's take a slightly simpler example.

syms x a

f(x) = a*x;

y = f(2)

y =

When I create y, MATLAB substitutes 2 in place of x in the symfun body. Giving a value to the variable a after f(x) has been created doesn't change f(x).

a = 3;

z = f(2)

z =

Using subs to substitute the numeric value of a into z will perform the substitution.

z2 = subs(z) % or subs(z, 'a', a)
z2 = 6

Alternately you could make your function a function of multiple symbolic variables:

syms w b

g(w, b) = b*w;

evaluateWithValueForw = g(4, b)

evaluateWithValueForw =

evaluateWithValueForb = g(w, 5)

evaluateWithValueForb =

evaluateWithValueForBoth = g(4, 5)

evaluateWithValueForBoth =

20

3 个评论
显示 1更早的评论隐藏 1更早的评论

Steven Lord 2021-1-26

If the symbolic expression does not contain any symbolic variables, use double to convert it to a double array. If it does contain symbolic variables, use vpa.

연승 김 2021-1-27

Wow!!!!! Thank you!!

"double" works!!!

I had to spend too much time on this trouble. uu...

Thank you again!

Happy new year and have a nice day~! smile^^

请先登录，再进行评论。

Answer 2

SaiDileep Kola 2021-1-19

0
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/717138-how-can-i-get-a-calculated-function-value#answer_601159

I see no reason why it is not calculated after declaring all values, check if values "u" and "v" are present in the workspace and try to run the equation once again if you see those values are present.