求助，matlab second derivative approximation,导数逼近

splelvis

clear all;
# ?) m% i; O9 O- V5 L/ g4 W0 b0 I7 P2 Qnx=50;
. z5 k" S3 J) }4 bny=30;
, G+ X" J& ~, F$ ~  g0 G) Q* j3 ahx=pi/nx;
1 M7 M7 {# s( Z/ [x=linspace(0,pi,nx+1);
9 F. C2 i& _) u7 Hy=linspace(0,pi,ny+1);
x_plus_h=x+hx.*ones(1,nx+1);
- |3 v; {8 E  u4 S) w; T4 J) M2 X: P7 Ex_minus_h=x-hx.*ones(1,nx+1);
) G; ?; d2 c9 Y* v2 z( ]. Jfor i=1:nx+1
, a8 A0 X7 _% [* q8 T    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)
( r4 a4 W" D! s) i# A! b3 l    end;
: `6 r2 t6 Z& ]+ N- Q7 o. M: Hend;
. X! l! a" n3 B1 H# b/ G[xx,yy]=meshgrid(x,y);
# T$ v$ T; K  X0 Tsurf(xx,yy,f_xx);
title('partial derivative w.r.t.xx')
  I, @- J' `% B，
: ?. |2 D( ^5 m* _
6 w: E* }* f2 ?6 M  E* V( |4 {另开一个f9文件，
function l=f9(x,y)
l=exp(sin(x-y));
: o0 k4 G" B5 b6 O+ m$ V; T6 D

% W- `7 w5 R5 m3 a- i8 x+ J然后出来说错误了，
8 }& x/ H7 P. \; C3 O3 u" c??? Input argument "x" is undefined.
+ z' H. Z) n  a; K' r3 u# P6 X* b
Error in ==> f9 at 2
l=exp(sin(x-y));
# t- Q. Z( r7 `' @7 O8 g: B6 {% fError 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);
  t. w1 y0 c0 N- V0 I
. A" S6 N: ?% i$ c% w8 o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~~~~~~~~~~~~~~~`