How to convert symbolic calculation to numeric?

Hi, I want to convert symbolic calculations into numeric one and substitute in the MATLAB program. This is because symbolic computation is taking a lot of time to do. Is there any way to convert symbolic calculation into numeric? Also I have one more question. I defined a function

f=sym('x1^2+2*x2^2+2*x3^2+2*x1*x2+2*x2*x3')
p=[1,1,1];
t2=p(1);
t2=evalAt(f,[x1=p(1),x2=p(2),x(3)=p(3),a=b]);

MATLAB gives error. I really don't understand what is problem. We do such substitutions in other matrices a=p(1) and so on. Why is this error? Really hard time for me. People, please help.

Answer 1

[Walter Roberson]

Where did you do the

syms x1 x2 x(3) a

Also note that your expression uses x3 but your evalAt uses x(3)

[Amit Kumar]

Hi, Yes I indeed made a mistake. But even after modifying, there seems errors. New code:

 syms x1 x2 x3 a

f=sym('x1^2+2*x2^2+2*x3^2+2*x1*x2+2*x2*x3')
p=[1,1,1];
t2=p(1);
t2=evalAt(f,[x1=p(1),x2=p(2),x3=p(3),a=b]);

[A Jenkins]

Did you define 'b' somewhere?

[Walter Roberson]

evalAt is a MuPAD function that has no direct MATLAB interface. If you want to use it you will need to use feval() or evalin()

t2 = feval('evalAt', f, {x1=p(1),x2=p(2),x3=p(3),a=b});

For your other question, look at matlabFunction()

[Amit Kumar]

A Jenkins: My mistake, I did define b but forgot to put in this code. Thanks for this!

Walter Roberson: Thank you very much providing some solution. I was trying really hard to get this. Thanks!