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nx=50;

ny=30;

hx=pi/nx;

x=linspace(0,pi,nx+1);

y=linspace(0,pi,ny+1);

x_plus_h=x+hx.*ones(1,nx+1);

x_minus_h=x-hx.*ones(1,nx+1);

for i=1:nx+1

for j=1:ny+1

f_xx(j,i)=(f9(x_plus_h(i),y(j))-2*f9+f9(x_minus_h(i),y(j)))./(hx.^2);

end;

end;

[xx,yy]=meshgrid(x,y);

surf(xx,yy,f_xx);

title('partial derivative w.r.t.xx')

,

and the other new document,f9,

function l=f9(x,y)

l=exp(sin(x-y));

and then the system said have error,

??? Input argument "x" is undefined.

Error in ==> f9 at 2

l=exp(sin(x-y));

Error in ==> partial_derivxx at 11

f_xx(j,i)=(f9(x_plus_h(i),y(j))-2*f9+f9(x_minus_h(i),y(j)))./(hx.^2);

where should i corrected to make it work?

thanks

anyone can help

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# Matlab second derivative approximation

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