error using double(subs())

Question

alice W 2019-7-4

0
链接

此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/470199-error-using-double-subs

编辑： alice W 2019-7-4

采纳的回答： Aiswarya Subramanian

EUfin_compute.m

在 MATLAB Online 中打开

Hello!

% full code please see EUfin_compute.m
syms x1 x2 x3 x4
EUfinsym=(10000*((1051*x3)/20000 + (1051*x4)/5000)*((1051*x3)/40000 + (1051*x4)/10000)*((23*((1051*x3)/20000 + (1051*x4)/5000)*((1051*x3)/40000 +.....
temp1=vpa(subs(EUfinsym, [x1 x2 x3 x4], [0.3 0.1 0.4 0.2]),6);
EUfin=double(temp1);

I got an error, how did that happen?

Error using symengine
Unable to convert expression into double array.
Error in sym/double (line 672)
        Xstr = mupadmex('symobj::double', S.s, 0);

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Answer 1

Aiswarya Subramanian 2019-7-4

0
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/470199-error-using-double-subs#answer_381939

Hello Alice,

double() cannot be used to convert symbolic expressions. You can instead use vpa() (Variable-Precision Arithmetic). Can you try the following and see if the error still persists?

EUfin=vpa(temp1);

You can also change the precision of vpa() by adding a second Argument to specify the amount of significant Digits. I hope this helps you!