求助，matlab second derivative approximation,导数逼近

splelvis

clear all;
. T! Z2 y5 y1 c) ]; Anx=50;
ny=30;
hx=pi/nx;
( a$ l% z! d8 q6 y: \! Gx=linspace(0,pi,nx+1);
+ r: V1 o) q5 r2 ty=linspace(0,pi,ny+1);
. a3 y$ `/ `8 |0 B  [x_plus_h=x+hx.*ones(1,nx+1);
x_minus_h=x-hx.*ones(1,nx+1);
7 t5 y  M, F) q& L3 B* [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);   %原式f(x+hx,y)-2f(x,y)+f(x-hx,y)./(hx^2)
    end;
end;
  X- l9 s1 \) b2 u; p, t# c, b[xx,yy]=meshgrid(x,y);
/ G: t( C. [' k7 Q+ rsurf(xx,yy,f_xx);
title('partial derivative w.r.t.xx')
，

另开一个f9文件，
function l=f9(x,y)
$ z% `. i7 T6 v5 @7 Al=exp(sin(x-y));
$ U3 U* \3 u& Q6 i
* W6 X% x6 ?" p& [- ^0 v2 [) j
然后出来说错误了，
??? Input argument "x" is undefined.

Error in ==> f9 at 2
l=exp(sin(x-y));
5 b& r- g6 @/ q- L$ |Error in ==> partial_derivxx at 11
6 I$ X2 f' `3 d8 b2 m, l        f_xx(j,i)=(f9(x_plus_h(i),y(j))-2*f9+f9(x_minus_h(i),y(j)))./(hx.^2);
! Q. U2 J0 l6 e0 P
各位要怎么改才对呢

splelvis

我自己找到了问题，f9应该是 f9(x(i),y(j))

douglas8j

abc~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

splelvis

不好意思，我也觉得自己太粗心了

douglas8j

henhaodeyipianwenzhang~~~~~~~~~~~~~~~`