Extracting numeric values from symbolic variables

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ali akbar
ali akbar 2020 年 9 月 6 日
回答済み: Alphonce Owayo 2021 年 2 月 23 日
I have two matrices say
x=[2 4 9 10];
syms c [1 4];
x==c
it returns
2=c1
4=c2
9=c3
10=c4
However when I write c1 in command window, it returns symbolic 'c1'.
I wanted to extract these numeric values or assign these values to c vector. How one would go around this.

採用された回答

Thiago Henrique Gomes Lobato
Thiago Henrique Gomes Lobato 2020 年 9 月 6 日
編集済み: Thiago Henrique Gomes Lobato 2020 年 9 月 6 日
x==c
The "==" operator is normally used as a logic comparison operation, not an assignment. In the case of using symbolic variables, "==" defines an equation, which could be solved, for example, with the matlab function solve. If you want to give values to your variables, use only one "=" sign, for example:
x=[2 4 9 10];
syms c [1 4];
>> c(1) = 2
c =
[ 2, c2, c3, c4]
>> c=x
c =
2 4 9 10
  2 件のコメント
Thiago Henrique Gomes Lobato
Thiago Henrique Gomes Lobato 2020 年 9 月 6 日
You're right, it becomes an equation when it contain symbolic variables. Since I believe he was knew to matlab I thought the more general definition of the operator would be easier to understand/apply to future cases. I will edit the answer accordingly

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その他の回答 (3 件)

madhan ravi
madhan ravi 2020 年 9 月 6 日
== forms an equation , it DOESN’T assign any values.
  1 件のコメント
madhan ravi
madhan ravi 2020 年 9 月 6 日

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Alphonce Owayo
Alphonce Owayo 2021 年 2 月 23 日
For example;
syms x y
eqn1=x+y==20;
eqn2=2.3x-9y==13;
soln=vpasolve(eqn1,eqn2);
xsoln=soln.x;
ysoln=soln.y;
or
xsoln=double(soln.x);
ysoln=double(son.y);
disp(xsoln);
disp(ysoln);

Alphonce Owayo
Alphonce Owayo 2021 年 2 月 23 日
shown above is how to extract numeric values from symbolic variables and display them in the command window.

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