MATLAB: Index exceeds the number of array elements (1)

I dont see any problem but, the command window just respond me

####>> EJsteepest

Index exceeds the number of array elements (1).

Error in EJsteepest>@(x)x(1)^3+3*x(1)*x(2)^2-15*x(1)+12*x(2) (line 5)

f = @(x) x(1)^3+3*x(1)*x(2)^2-15*x(1)+12*x(2);

Error in steepest_descent (line 4)

f_hat = f(x_hat);

Error in EJsteepest (line 12)

#######

steepest_descent(f,a,b,x1,E, lambda, delta)
function x_star = steepest_descent(f,a,b,x1,E, lambda, delta)
m = 1;
x_hat =x1;
f_hat = f(x_hat);
I = eye(length(a));
x=zeros(1,length(a));%fila de ceros de 1 hasta j
d=zeros(1,length(a));
while lambda > E
    if m > 0 
        for j = 1:length(a)
            d(j) = (f(x_hat + delta*I(j,:))- f(x_hat - delta*I(j,:)))/2*delta;
        end
        d=-d/norm(d);
        m=0;
    end
    for j=1:length(a)
        x(j)=min(max(x_hat(j)+lambda*d(j),a(j)),b(j));
    end
    f_x = f(x);
    if f_x < f_hat
        while f_x< f_hat
            x_hat = x;
            f_hat = f_x;
            for j=1:length(a)
                x(j)=min(max(x_hat(j)+lambda*d(j),a(j)),b(j));
            end
            f_x = f(x);
        end
        m=1;
    else
        lambda = lambda/2;
    end
end
x_star = x_hat;                
end
##########NEXT SCRIP
f = @(x) x(1)^3+3*x(1)*x(2)^2-15*x(1)+12*x(2);
a=[3/2 -3/2];
b=[3 0];
E = 10^-1;
lambda=1/2;
x1=(1 -0.3);
delta=10^-2;
steepest_descent(f,a,b,x1,E, lambda, delta)

Answer 1

[Walter Roberson]

x1=(1 -0.3);

That is not a vector: it is 1 minus 0.3 .

x1=[1, -0.3];

[diego sanchez torralba]

it was this, thank you

Answer 2

[KSSV]

You are trying to extract more number of elements then present in the array.

Example:

A = rand(1,3) ;    
A(1) % no error
A(3) % no error
A(4)   % error, becuase there is no 4th element in A 

In the same note check, the function

f = @(x) x(1)^3+3*x(1)*x(2)^2-15*x(1)+12*x(2);

It seems in your case x is a scalr and is not of size 1*2.

[diego sanchez torralba]

i was thinking that was my problem, but i dont see how to fix it in my program