求助，matlab second derivative approximation,导数逼近

splelvis

clear all;
nx=50;
( O8 n) }8 T$ g4 a; U$ E. m. ^6 H- Rny=30;
5 y$ U4 s" ]) X- ?$ f; [3 dhx=pi/nx;
x=linspace(0,pi,nx+1);
y=linspace(0,pi,ny+1);
x_plus_h=x+hx.*ones(1,nx+1);
& |3 ?; `! A& D  I; g6 }- Rx_minus_h=x-hx.*ones(1,nx+1);
for i=1:nx+1
    for j=1:ny+1
, o' s/ w( r5 k+ J  P9 U6 Y' |        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;
( R# U: `- t: z[xx,yy]=meshgrid(x,y);
+ e  G* e1 Y5 k  msurf(xx,yy,f_xx);
# ]* O+ S; ]# J" g5 @/ P) jtitle('partial derivative w.r.t.xx')
，

另开一个f9文件，
7 k* F0 o9 B+ r  hfunction l=f9(x,y)
l=exp(sin(x-y));

2 ]  U4 C8 Y/ U
1 d- G" B  b, O# J然后出来说错误了，
??? Input argument "x" is undefined.

Error in ==> f9 at 2
/ }' w- `# h6 b, ]  r5 f2 Il=exp(sin(x-y));
) k1 T1 i; A9 W/ Z" XError 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);
9 Y5 E- F5 d7 x( T: R
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~~~~~~~~~~~~~~~`