Variable q5 must be of size [1 2]. It is currently of size [1 1]. Check where the variable is assigned a value.

syms x y
f(x,y)=x-x*y^2+sqrt(y);
u=[2,9];
q5=dot(u/norm(u),jacobian(f(x,y),[x,y]));

[lateef]

how do i make q5 be of size [1,2]

Answer 1

[Walter Roberson]

syms x y
f(x,y)=x-x*y^2+sqrt(y);
u = sym([2,9]);
part1 = u/norm(u)

part1 = 

part2 = jacobian(f(x,y),[x,y])

part2 = 

q5 = dot(part1, part2)

q5 = 

You have the dot product of a 1 x 2 and a 1 x 2. The result is going to be 1 x 1. You should not expect anything different for that set of equations.

[lateef]

even with this code that you provided i get the same error message that states Variable q5 must be of size [1 2]. It is currently of size [1 1]. Check where the variable is assigned a value

[lateef]

Variable q5 must be of size [1 2]. It is currently of size [1 1]. Check where the variable is assigned a value.

[Walter Roberson]

The point is that the outcome for those operations must be [1 1], never [1 2]. There is no way to have the outcome be [1 2] -- not unless what you are intended to program is something different..

[lateef]

with that being said what in the code is incorect // the original question states assign f(x,y)=x-xy^2+sqrt(y) Find delta f(2,9) and assign the result to q5

[Torsten]

What is delta f(2,9) ? The gradient of f in (2,9) ?

syms x y
f=x-x*y^2+sqrt(y);
q5 = subs(jacobian(f),[x y],[2,9])

q5 = 

[lateef]

this worked thank you !