I want to find the value of k

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SANDIPKUMAR ROYADHIKARI
SANDIPKUMAR ROYADHIKARI on 23 Oct 2021
syms x1 x2 x3
x=[x1;x2;x3];
f1=x(1)^3+12*x(2)+1;
f2=x(2)^9+5*x(1)-3;
f3=x(2)*x(3)^2+8;
k=[diff(f1,x(1)),diff(f1,x(2)),diff(f1,x(3));diff(f2,x(1)),diff(f2,x(2)),diff(f2,x(3));diff(f3,x(1)),diff(f3,x(2)),diff(f3,x(3))];
x=[2;5;9];
With these values of x
I want to find out the value of k, how do I do that ?

Answers (1)

John D'Errico
John D'Errico on 23 Oct 2021
syms x1 x2 x3
x=[x1;x2;x3];
f1=x(1)^3+12*x(2)+1;
f2=x(2)^9+5*x(1)-3;
f3=x(2)*x(3)^2+8;
Here is the matrix k.
k=[diff(f1,x(1)),diff(f1,x(2)),diff(f1,x(3));diff(f2,x(1)),diff(f2,x(2)),diff(f2,x(3));diff(f3,x(1)),diff(f3,x(2)),diff(f3,x(3))]
k = 
So, a function of x1, x2, and x3.
Why did you define x as x=[x1;x2;x3];, when you never used it again?
If you wish to substitute for x1, x2, x3, you could do this:
subs(k,[x1,x2,x3],[2 5 9])
ans = 

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