求助，matlab second derivative approximation,导数逼近

splelvis

clear all;
nx=50;
8 ~9 Q% h1 p8 Gny=30;
hx=pi/nx;
6 I0 |) p/ ^6 J0 H! ~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
  f0 l4 \, f( [0 P) V2 C$ q    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;
9 d% y1 ^; u) {% Wend;
[xx,yy]=meshgrid(x,y);
+ e- e! P: M" J" W2 esurf(xx,yy,f_xx);
title('partial derivative w.r.t.xx')
/ k( k" B, M( R0 c，

另开一个f9文件，
( L) U/ H/ J$ D9 kfunction l=f9(x,y)
4 s+ k4 i) w! U1 N* C6 ^+ Ml=exp(sin(x-y));


然后出来说错误了，
??? Input argument "x" is undefined.
4 `3 \! O, V$ `& C7 W4 }: ~. N  z
Error in ==> f9 at 2
  C4 Z+ u1 E. T4 `l=exp(sin(x-y));
4 ?( F+ s6 N" ^0 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);
' J1 h, o; R' p9 }+ b
4 S% n2 X0 Q7 G: Z5 ]2 q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~~~~~~~~~~~~~~~`