求助，matlab second derivative approximation,导数逼近

splelvis

clear all;
+ k# n- K0 K: [$ t( pnx=50;
ny=30;
hx=pi/nx;
' L/ U* {3 ?4 C  x1 N# [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);
0 e& z0 M; A: a6 \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;
" I% S5 t! }- {1 Q4 r; [# f- ~6 i[xx,yy]=meshgrid(x,y);
( c- `8 A0 [: L1 O0 u- E& \: I0 msurf(xx,yy,f_xx);
title('partial derivative w.r.t.xx')
，
( [$ @' f6 _& B5 n/ l
另开一个f9文件，
function l=f9(x,y)
7 S! c1 o  I* i9 _: ~l=exp(sin(x-y));
" |1 S9 Q4 w, h
4 J* U# f( u" p4 h# G! i! I4 i% {
然后出来说错误了，
$ H! W' t7 b/ t6 F2 s8 Q2 R) S. O+ U/ ~??? Input argument "x" is undefined.
, q  `& D/ _4 E' M
* p6 p# X- A6 V6 x# qError in ==> f9 at 2
l=exp(sin(x-y));
Error in ==> partial_derivxx at 11
8 U5 m- X4 a& P7 J( w( ~        f_xx(j,i)=(f9(x_plus_h(i),y(j))-2*f9+f9(x_minus_h(i),y(j)))./(hx.^2);
5 v% ~* b" h' @" x+ p, d
( g( g6 f% U& A- ~6 e3 n- y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~~~~~~~~~~~~~~~`