error using double(subs())

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);

Answer 1

[Aiswarya Subramanian]

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!

[alice W]

Thank you very much!

I have found my mistake. Use eval() is OK.

eval(sub())

Ref:

https://stackoverflow.com/questions/20032441/evaluate-matlab-symbolic-function