求助，matlab second derivative approximation,导数逼近

splelvis

clear all;
nx=50;
ny=30;
# c' T+ l4 d- f# }$ B  v7 ]6 j7 o- rhx=pi/nx;
1 Z+ m/ k5 U7 D' A  Ux=linspace(0,pi,nx+1);
2 b+ Z, q$ x! {/ |0 q1 Z& ry=linspace(0,pi,ny+1);
' z6 z6 d5 r( d6 S. dx_plus_h=x+hx.*ones(1,nx+1);
x_minus_h=x-hx.*ones(1,nx+1);
6 @0 u8 l6 x  i+ B" Yfor i=1:nx+1
* _- R+ `  }. j# ~5 J( x    for j=1:ny+1
9 i3 I6 _$ [6 e% u$ ^: S        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)
) E2 x1 H- M0 Q    end;
  B. f" i# L$ h* aend;
[xx,yy]=meshgrid(x,y);
surf(xx,yy,f_xx);
title('partial derivative w.r.t.xx')
，
/ O8 K, P! F! F& R- q
' e: J2 r  Y0 N3 B% {另开一个f9文件，
( o5 {" i4 y7 P- X1 Qfunction l=f9(x,y)
, F/ e0 Y1 }1 ^2 El=exp(sin(x-y));


然后出来说错误了，
??? Input argument "x" is undefined.

Error in ==> f9 at 2
l=exp(sin(x-y));
" ]; l# d. h/ {9 k9 ~4 K7 oError 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);

$ n6 g% t7 i& g3 j各位要怎么改才对呢

douglas8j

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

splelvis

不好意思，我也觉得自己太粗心了

douglas8j

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

splelvis

我自己找到了问题，f9应该是 f9(x(i),y(j))