Minimize banana function with steepest descent algorithm

I write this code to minimize banana function but its not working.can any body help me please?

clear;clc;

banana=@ (x,y) (100*(y-x^2)^2+(1-x)^2); x0=100; y0=50;

dx=0.001; dy=0.001;

error=0.0001;

g=[inf;inf];

number_of_iteration=0; grad_x=@(x,y) (300*x^2-400*x*y+2*x-2); grad_y=@(x,y) (200*(y-x^2)); banana0=banana(x0,y0); grad_x0=grad_x(x0,y0); grad_y0=grad_y(x0,y0);

while norm(g)>error

    gx=grad_x(x0,y0);
    gy=grad_y(x0,y0);

    alpha_x=gx*dx;
    alpha_y=gy*dy;

    g=[gx;gy];

    x0=x0-alpha_x;
    y0=y0-alpha_y;

    number_of_iteration=number_of_iteration+1;

end fprintf('number of iterations until convergence is =%3i\n',(number_of_iteration));