求助，matlab second derivative approximation,导数逼近

splelvis

clear all;
2 |$ Y1 n; ~, B9 K* Y2 `% n- [  n6 Tnx=50;
% a; \7 F* }3 _; k$ tny=30;
' w2 U; f+ n) ^$ L! I4 {hx=pi/nx;
1 ?4 l$ e  D- f. [8 {x=linspace(0,pi,nx+1);
9 W+ m) h; G* G/ [! b) ~& My=linspace(0,pi,ny+1);
x_plus_h=x+hx.*ones(1,nx+1);
8 Z4 J4 O( q0 t+ ?/ s4 Tx_minus_h=x-hx.*ones(1,nx+1);
1 t2 y' x. X8 V7 I" A; P9 N1 pfor i=1:nx+1
7 d, S5 I' i& B+ y' ]4 y2 y, _    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;
/ C- I- _* i! Nend;
% d) P4 y) b) }; N8 |[xx,yy]=meshgrid(x,y);
surf(xx,yy,f_xx);
title('partial derivative w.r.t.xx')
，
2 L, g( H* ^% q! K2 c
另开一个f9文件，
function l=f9(x,y)
: t; i4 V: y5 f9 [2 y+ S+ V! yl=exp(sin(x-y));

/ `, [& P* o, q3 h+ \9 r2 ~2 {/ x
然后出来说错误了，
??? Input argument "x" is undefined.

4 v2 n  W* q  m: E/ j9 qError in ==> f9 at 2
7 E2 ?! H- Y; }  P4 b! ml=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);

% \6 \) U4 _5 v; B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~~~~~~~~~~~~~~~`