求助，matlab second derivative approximation,导数逼近

splelvis

clear all;
nx=50;
* w: z$ A9 x% A: ^( B. Tny=30;
hx=pi/nx;
  B6 X7 Y% ?1 Q5 m0 z$ n5 [x=linspace(0,pi,nx+1);
! N! J8 F% C" C- a6 {+ P+ j3 jy=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
7 O$ |8 V- W9 b/ p" k7 j        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)
, h- x2 s# y3 y8 P9 S/ w    end;
) |  `7 k2 E0 }8 n9 e. D- Dend;
[xx,yy]=meshgrid(x,y);
! k/ \, C  m! |# h) ssurf(xx,yy,f_xx);
& W8 t$ [& U& C/ j- V: x) S5 S$ Wtitle('partial derivative w.r.t.xx')
，
0 T" b1 k. ]& z! W' s4 f7 |
另开一个f9文件，
function l=f9(x,y)
l=exp(sin(x-y));
1 C7 ]: Q9 _# c  a; B% r' L

然后出来说错误了，
??? Input argument "x" is undefined.
) V2 B3 e7 t. f- |; X: ]) m
; [1 b4 X# \5 x4 hError 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);

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~~~~~~~~~~~~~~~`