Calculate the gradient of a function

Hello. I want to calculate the gradient of the function :

g={@(x)-x;@(x)x-1;@(y)-y;@(y)y-1};

with the following command :

gradient(g, [x, y]);

but I get the following error :

Undefined function or variable 'x'.

How I should proceed? Thanks.

[John BG]

perhaps you would like to consider proceeding by defining x?

[amine&&]

Thanks john, Even if i define the variable that gives me an error. Thanks.

Answer 1

[Walter Roberson]

You are confusing the numeric gradient function http://www.mathworks.com/help/matlab/ref/gradient.html with the symbolic gradient function, http://www.mathworks.com/help/symbolic/gradient.html

On the other hand, neither gradient() accepts a vector or cell array of function handles. Numeric gradient() accepts a numeric vector or array, and spacing distances for each of the dimensions. Symbolic gradient() accepts a scalar symbolic expression or symbolic function together with the variables to take the gradient over.

When you have a vector of functions to work with, you almost certainly want a jacobian rather than a gradient. Symbolic jacobian http://www.mathworks.com/help/symbolic/jacobian.html accepts a symbolic expression, symbolic function, or symbolic vector (but not a cell array of function handles.)

[amine&&]

Thanks Roberson, i think the following command is just :

jacobian([-x, x-1, -y, y-1], [x, y])

Thanks.

[Walter Roberson]

You would have to have

syms x y

first.

[amine&&]

Ok Roberson. Thanks!

Answer 2

[garrett batt]