Variable x must be of data type double. It is currently of type sym. Check where the variable is assigned a value.

Question

Jonas Freiheit 2020-9-17

0
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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/595189-variable-x-must-be-of-data-type-double-it-is-currently-of-type-sym-check-where-the-variable-is-ass

编辑： Ameer Hamza 2020-9-19

Hello,

I was wondering how I could change my variable 'x' to type double from syms. I've tried converting it to type double with x=double(x) and nothing has happened.

Help would be very appreciated!

U = [3,2,1;
     0,1,2;
     0,0,1]
b = [0;0;0]
x=backsub(A,b)
function x = backsub_syms(U,b)
n = length(b);
syms t
x=sym(zeros(n,1))
x(n)=sym('t')
b=(sym(b))
for i = n:-1:1
    x(i)=b(i);
    x(n)=sym('t')
    if i<n
        for j = n:-1:i+1
            
            x(i)=x(i)-U(i,j)*x(j);
            
        end
    end
    
    x(i)=x(i)/U(i,i);
end
end

Thanks for the help much appreciated!

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Answer 1

Ameer Hamza 2020-9-19

0
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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/595189-variable-x-must-be-of-data-type-double-it-is-currently-of-type-sym-check-where-the-variable-is-ass#answer_497227

编辑：Ameer Hamza 2020-9-19

在 MATLAB Online 中打开

You need to substitute a value for symbolic variable t to get a numeric value

U = [3,2,1;
     0,1,2;
     0,0,1];
b = [0;0;0];
syms t;
x = backsub_syms(U,b);
y = subs(x, t, 1) % t = 1
double(y)
function x = backsub_syms(U,b)
n = length(b);
syms t
x=sym(zeros(n,1))
x(n)=sym('t')
b=(sym(b))
for i = n:-1:1
    x(i)=b(i);
    x(n)=sym('t')
    if i<n
        for j = n:-1:i+1
            
            x(i)=x(i)-U(i,j)*x(j);
            
        end
    end
    
    x(i)=x(i)/U(i,i);
end
end