求助，matlab second derivative approximation,导数逼近

splelvis

clear all;
nx=50;
ny=30;
hx=pi/nx;
) T, ?: E' R2 y) B6 \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
: S& K4 C. z, d    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;
2 u9 ~2 ^8 E0 C3 e8 p/ f# H3 C$ ^end;
[xx,yy]=meshgrid(x,y);
3 ?4 D" d3 n* R( v  Ksurf(xx,yy,f_xx);
title('partial derivative w.r.t.xx')
，
2 x) @  R6 ^& {( \" d6 l/ V' K
# v4 L+ u1 A2 z0 [6 {) x$ C( K另开一个f9文件，
- z) D2 M  M2 d9 K& U! W5 Rfunction l=f9(x,y)
7 O5 k' W& S$ d6 r" kl=exp(sin(x-y));
8 u/ H# t+ m6 W" s" P- x

1 \( \/ K5 g& e6 Z. j# G然后出来说错误了，
/ B6 P0 i2 W' ^+ B  n??? Input argument "x" is undefined.
3 z5 v; L0 _% l; ^% {" r
Error in ==> f9 at 2
5 l2 h% r9 W- ~  E* yl=exp(sin(x-y));
& \; E; U! c9 Z8 _( Y1 VError in ==> partial_derivxx at 11
. V6 H: w- Y: v4 Z5 M4 z! ?        f_xx(j,i)=(f9(x_plus_h(i),y(j))-2*f9+f9(x_minus_h(i),y(j)))./(hx.^2);

" f+ F% g; Y# U" n  q0 D5 Q! U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~~~~~~~~~~~~~~~`